Methyl-CpG-binding protein 2 polymorphisms and vulnerability to autism.

The methyl-binding protein gene, MECP2, is a candidate for involvement in autism through its implication as a major causative factor in Rett syndrome that has similarities to autism. Rare mutations in MECP2 have also been identified in autistic individuals. We have examined the possible broader involvement of MECP2 as a predisposing factor in the disorder. Analysis of polymorphic markers spanning the gene and comprising both microsatellites and single nucleotide polymorphisms (SNPs) by the transmission disequilibrium test in two collections of families (219 in total), one in the USA and one in the UK, has provided evidence for significant association (P = 0.009) for a three-marker SNP haplotype of MECP2 with autism/autism spectrum disorders. This association is supported by association of both Single Sequence Repeat (SSR) and SNP single markers located at the 3' end of the MECP2 locus and flanking sequence, the most significant being that of an indel marker located in intron 2 (P = 0.001 - Bonferroni corrected P = 0.006). This suggests that one or more functional variants of MECP2 existing at significant frequencies in the population may confer increased risk of autism/autism spectrum disorders and warrants further investigation in additional independent samples.

Aging changes of the choroidal dye filling pattern in indocyanine green angiography of normal subjects.

PURPOSE: To study the aging changes in the choroid of healthy volunteers with indocyanine green (ICG) angiography. METHODS: Video ICG angiography with adjunctive computer-assisted image analysis was performed on 35 eyes of 30 healthy volunteers (age range, 21-81 years; mean +/- standard deviation, 50.5 +/- 16.2 years) to observe the aging changes of the choroid. RESULTS: In patients in the second and third decades of life, the subfoveal choroidal arterioles fluoresced initially with subsequent rapid filling of the feeding arterioles and choriocapillaris. The watershed zone was clearly observed. In patients older than age 50, the choroidal vasculature filled more slowly. Eventually, the margin of the watershed zone became blurred. The quantitative analysis showed that the number of choroidal arterioles and the fluorescent intensity in the macular region were reduced with age (P < 0.005). In the early venous phase, hypofluorescent patches seen in all ages increased in size and number and remained with aging. The mean fluorescence intensity was not correlated statistically with age. CONCLUSIONS: The features of normal aging patterns of the choroid that we investigated are essential to the interpretation of ICG angiography and may help in understanding the physiologic and pathologic conditions of the choroidal circulations and the choroid and retina themselves.

Insights into the molecular mechanism of p53 inhibition by HTLV type 1 Tax.

The p53 protein plays a pivotal role in transmitting signals from many forms of genotoxic stress to genes and factors that control aspects of the cell cycle and death. Although mutated in approximately 60% of all human cancers, only a minority of human T-lymphotropic virus type 1 (HTLV-1)-transformed cells carry p53 mutations. Nevertheless, the p53 protein in HTLV-1-transformed cells is functionally inactive. We have previously demonstrated that the HTLV-1 Tax protein can inhibit p53 trans-activation function. Tax does not accomplish this by directly binding to p53, but rather by a unique mechanism that includes constitutive phosphorylation of p53 at Ser-15 and Ser-392. Analysis of Tax mutants in lymphocytes demonstrates that Tax-induced p53 inhibition correlates with the ability of Tax to activate NF-kappaB, but not p300 binding or CREB trans-activation. Consistent with these results, expression of the I-kappaBalpha(S32,36A) mutant that blocks NF-kappaB activation blocks Tax-mediated p53 inhibition. We further demonstrate the importance of Tax activation of NF-kappaB in p53 inhibition, using p65 knockout (KO) mouse embryo fibroblasts (MEFs). In the absence of p65 Tax could not inhibit p53. Tax does activate IKKbeta in the p65 KO MEFs, indicating that prenuclear events of NF-kappaB activation are not sufficient for Tax-mediated p53 inhibition, but rather NF-kappaB transcriptional activation is critical. Importantly, using phosphospecific antibodies, we demonstrate that phosphorylation of p53 at Ser-15 and Ser-392 correlates with Tax-mediated inhibition. In addition, mutation of p53 at Ser-15 and Ser-392 to alanines renders p53 resistant to Tax inhibition. This report reviews p53 inhibition by Tax and presents our current model.

Inactivation of p53 by human T-cell lymphotropic virus type 1 Tax requires activation of the NF-kappaB pathway and is dependent on p53 phosphorylation.

p53 plays a key role in guarding cells against DNA damage and transformation. We previously demonstrated that the human T-cell lymphotropic virus type 1 (HTLV-1) Tax can inactivate p53 transactivation function in lymphocytes. The present study demonstrates that in T cells, Tax-induced p53 inactivation is dependent upon NF-kappaB activation. Analysis of Tax mutants demonstrated that Tax inactivation of p53 function correlates with the ability of Tax to induce NF-kappaB but not p300 binding or CREB transactivation. The Tax-induced p53 inactivation can be overcome by overexpression of a dominant IkappaB mutant. Tax-NF-kappaB-induced p53 inactivation is not due to p300 squelching, since overexpression of p300 does not recover p53 activity in the presence of Tax. Further, using wild-type and p65 knockout mouse embryo fibroblasts (MEFs), we demonstrate that the p65 subunit of NF-kappaB is critical for Tax-induced p53 inactivation. While Tax can inactivate endogenous p53 function in wild-type MEFs, it fails to inactivate p53 function in p65 knockout MEFs. Importantly, Tax-induced p53 inactivation can be restored by expression of p65 in the knockout MEFs. Finally, we present evidence that phosphorylation of serines 15 and 392 correlates with inactivation of p53 by Tax in T cells. This study provides evidence that the divergent NF-kappaB proliferative and p53 cell cycle arrest pathways may be cross-regulated at several levels, including posttranslational modification of p53.

Cell cycle-regulated transcription by the human immunodeficiency virus type 1 Tat transactivator.

Cyclin-dependent kinases are required for the Tat-dependent transition from abortive to productive elongation. Further, the human immunodeficiency virus type 1 (HIV-1) Vpr protein prevents proliferation of infected cells by arresting them in the G(2) phase of the cell cycle. These findings suggest that the life cycle of the virus may be integrally related to the cell cycle. We now demonstrate by in vitro transcription analysis that Tat-dependent transcription takes place in a cell cycle-dependent manner. Remarkably, Tat activates gene expression in two distinct stages of the cell cycle. Tat-dependent long terminal repeat activation is observed in G(1). This activation is TAR dependent and requires a functional Sp1 binding site. A second phase of transactivation by Tat is observed in G(2) and is TAR independent. This later phase of transcription is enhanced by a natural cell cycle blocker of HIV-1, vpr, which arrests infected cells at the G(2)/M boundary. These studies link the HIV-1 Tat protein to cell cycle-specific biological functions.

The coactivator CBP stimulates human T-cell lymphotrophic virus type I Tax transactivation in vitro.

Tax interacts with the cellular cyclic AMP-responsive element binding protein (CREB) and facilitates the binding of the coactivator CREB binding protein (CBP), forming a multimeric complex on the cyclic AMP-responsive element (CRE)-like sites in the human T-cell lymphotrophic virus type I (HTLV-I) promoter. The trimeric complex is believed to recruit additional regulatory proteins to the HTLV-I long terminal repeat, but there has been no direct evidence that CBP is required for Tax-mediated transactivation. We present evidence that Tax and CBP activate transcription from the HTLV-I 21 base pair repeats on naked DNA templates. Transcriptional activation of the HTLV-I sequences required both Tax and CBP and could be mediated by either the N-terminal activation domain of CBP or the full-length protein. Fluorescence polarization binding assays indicated that CBP does not markedly enhance the affinity of Tax for the trimeric complex. Transcription analyses suggest that CBP activates Tax-dependent transcription by promoting transcriptional initiation and reinitiation. The ability of CBP to activate the HTLV-I promoter does not involve the stabilization of Tax binding, but rather depends upon gene activation properties of the co-activator that function in the context of a naked DNA template.

The improved image of indocyanine green angiography in young healthy volunteers.

PURPOSE: The authors performed indocyanine green (ICG) angiography in healthy volunteers using a high resolution ICG video system to obtain baseline images for subsequent studies. METHODS: Ten eyes of 10 healthy, young volunteers were studied. Before ICG angiography, all eyes were examined ophthalmoscopically and biomicroscopically and found to be intact. Indocyanine green (50 mg) dissolved in 2 mL of distilled water was injected through the antecubital vein. Video ICG angiogram was recorded until 30 minutes after the dye injection. RESULTS: Although the choroidal dye filling varied among subjects, it always began in the macular area. In the 10 volunteers, initial dye filling had two patterns: flush (n = 2) and reticular (n = 8). Patchy dye-filling delay in the posterior fundus was a common finding (n = 9). Vertical filling delay running between the medial and nasal cilial arteries was observed in nine eyes. The choroidal circulation filled completely before the retinal circulation did. At 30 minutes after dye injection, interstitial tissue staining of the choroid and vascular silhouette resulting from dye washout was observed in all eyes. CONCLUSIONS: Arterioles and capillaries of the choroid were well delineated by ICG angiography, resulting in better understanding of the physiologic and pathologic conditions of the choroidal circulations and the chorioretina itself.

Parents' sense of "entitlement" in adoptive and nonadoptive families.

The literature suggests that problems with developing a sense of entitlement are unique to adoptive families, but this assumption has not been examined empirically. In this study, a questionnaire was constructed to define operationally those characteristics associated with the construct of entitlement, and was administered to adoptive and nonadoptive families with children averaging 11.5 years in age who presented either for mental health service or were recruited as a comparison-control sample. Factor analysis yielded four factors on which the four groups of subjects were compared. Results indicated that problems with entitlement are not specific to adoptive families. Instead, differences in sense of entitlement occurred primarily between clinic and nonclinic control families, regardless of whether the target child had been adopted. Findings are discussed in terms of methodological shortcomings in the adoption research literature and how problems in entitlement may be associated with other family characteristics.

Interaction of the human T-cell lymphotropic virus type 1 tax transactivator with transcription factor IIA.

The Tax protein of human T-cell lymphotropic virus type 1 (HTLV-1) is a 40-kDa transcriptional activator which is critical for HTLV-1 gene regulation and virus-induced cellular transformation. Tax is localized to the DNA through its interaction with the site-specific activators cyclic AMP-responsive element-binding protein, NF-kappaB, and serum response factor. It has been suggested that the recruitment of Tax to the DNA positions Tax for interaction with the basal transcriptional machinery. On the basis of several independent assays, we now report a physical and functional interaction between Tax and the transcription factor, TFIIA. First, Tax was found to interact with the 35-kDa (alpha) subunit of TFIIA in the yeast two-hybrid interaction system. Importantly, two previously characterized mutants with point mutations in Tax, M32 (Y196A, K197S) and M41 (H287A, P288S), which were shown to be defective in Tax-activated transcription were unable to interact with TFIIA in this assay. Second, a glutathione-S-transferase (GST) affinity-binding assay showed that the interaction of holo-TFIIA with GST-Tax was 20-fold higher than that observed with either the GST-Tax M32 activation mutant or the GST control. Third, a coimmunoprecipitation assay showed that in HTLV-1-infected human T lymphocytes, Tax and TFIIA were associated. Finally, TFIIA facilitates Tax transactivation in vitro and in vivo. In vitro transcription studies showed reduced levels of Tax-activated transcription in cell extracts depleted of TFIIA. In addition, transfection of human T lymphocytes with TFIIA expression vectors enhanced Tax-activated transcription of an HTLV-1 long terminal repeat-chloramphenicol acetyltransferase reporter construct. Our study suggests that the interaction of Tax with the transcription factor TFIIA may play a role in Tax-mediated transcriptional activation.

Interaction of human immunodeficiency virus type 1 Tat with a unique site of TFIID inhibits negative cofactor Dr1 and stabilizes the TFIID-TFIIA complex.

We have previously reported the direct physical interaction between the human immunodeficiency virus (HIV) type I Tat protein and the basal transcription factor TBP/TFIID. Affinity chromatography demonstrated that wild-type Tat, but not a transactivation mutant of Tat, was capable of depleting TBP/TFIID from cell extracts. These experiments represented the first demonstration of a basal transcription factor that binds, in an activation-dependent manner, to Tat. We now report that the Tat-TBP interaction can be detected in HIV type 1-infected cells. The domain of TBP interacting with Tat has been mapped from amino acids 163 to 196 by using deletion and site-specific mutants of TBP. This domain of TBP, which includes the HI and S2 domains, is distinct from the H2 binding site for other activator proteins, such as E1A. The interaction of Tat with TFIID regulates the binding of accessory proteins to TFIID. Tat stabilizes the interaction of TFIID with TFIIA in a gel shift assay. In addition, Tat competes for Dr1 interaction with TBP. Our results suggest that the basal transcription factor TBP/TFIID represents an important regulatory molecule in HIV transcription.

Transactivation of the human T-cell lymphotropic virus type 1 Tax1-responsive 21-base-pair repeats requires Holo-TFIID and TFIIA.

The human T-cell lymphotropic virus type 1 (HTLV-1) is the etiological agent for adult T-cell leukemia and tropical spastic paraparesis/HTLV-1-associated myelopathy. The HTLV-1 Tax1 gene product has been shown to transactivate transcription of viral and cellular promoters. To examine the biochemical mechanism of Tax1 transactivation, we have developed an in vitro transactivation assay in which wild-type Tax1 is able to specifically transactivate a polymerase II promoter through upstream Tax1-responsive elements. The in vitro system utilizes the HTLV-1 21-bp repeats cloned upstream of the ovalbumin promoter and G-free cassette. Purified Tax1 specifically transactivates this template 5- to 10-fold in a concentration-dependent manner. No transactivation of the ovalbumin promoter (pLovTATA) template control was observed. Tax1 transactivation was inhibited by low concentrations of alpha-amanitin and was effectively neutralized by anti-Tax1 but not control sera. Consistent with in vivo transactivating activity, Tax1 NF-kappa B mutant M22, but not cyclic AMP-responsive element-binding protein mutant M47, transactivated the template containing the tandem 21-bp repeat. In a reconstituted in vitro transcription assay, Tax1 transactivation was dependent upon basal transcription factors TFIIB, TFIIF, Pol II, TFIID, and TFIIA. TATA-binding protein did not functionally substitute for TFIID in the transactivation assay by Tax1 but was sufficient for basal transcription. Finally, we have used anti-TFIIA antibody (p55) to ask if Tax1 transactivation required TFIIA activity. Addition of TFIIA antibody to in vitro transcription reactions, as well as depletion of TFIIA by preclearing with antibody, showed that TFIIA was required for Tax1 transactivation. Only a slight (twofold) drop of basal transcription was observed. Tax1 transactivation was restored when purified HeLa TFIIA was added back into the reconstituted system. We propose that Tax1 utilizes a transactivation pathway involving the activator regulated basal transcription factors TFIID and TFIIA.

Transcription of the human T-cell lymphotropic virus type I promoter by an alpha-amanitin-resistant polymerase.

The human T-lymphotropic virus type I (HTLV-I) promoter contains the structural features of a typical RNA polymerase II (pol II) template. The promoter contains a TATA box 30 bp upstream of the transcription initiation site and binding sites for several pol II transcription factors, and long poly(A)+ RNA is synthesized from the integrated HTLV-I proviral DNA in vivo. Consistent with these characteristics, HTLV-I transcription activity was reconstituted in vitro by using TATA-binding protein, TFIIA, recombinant TFIIB, TFIIE, and TFIIF, TFIIH, and pol II. Transcription of the HTLV-I promoter in the reconstituted system requires RNA pol II. In HeLa whole cell extracts, however, the HTLV-I long terminal repeat also contains an overlapping transcription unit (OTU). HTLV-I OTU transcription is initiated at the same nucleotide site as the RNA isolated from the HTLV-I-infected cell line MT-2 but was not inhibited by the presence of alpha-amanitin at concentrations which inhibited the adenovirus major late pol II promoter (6 micrograms/ml). HTLV-I transcription was inhibited when higher concentrations of alpha-amanitin (60 micrograms/ml) were used, in the range of a typical pol III promoter (VA-I). Neutralization and depletion experiments with three distinct pol II antibodies demonstrate that RNA pol II is not required for HTLV-I OTU transcription. Antibodies to basal transcription factors TATA-binding protein and TFIIB, but not TFIIIC, inhibited HTLV-I OTU transcription. These observations suggest that the HTLV-I long terminal repeat contains overlapping promoters, a typical pol II promoter and a unique pol III promoter which requires a distinct set of transcription factors.

Transcriptional activation of minimal HIV-1 promoter by ORF-1 protein expressed from the SalI-L fragment of human herpesvirus 6.

The SalI-L fragment of human herpesvirus 6 (HHV-6) strain U1102 transformed rodent cells and transactivated the HIV-1 LTR 10- to 15-fold in both monkey fibroblasts and human T-lymphocytes. In this report, the SalI-L transactivator of the HIV-1 LTR was localized to ORF-1 which codes for a protein of 357 amino acids. To determine if ORF-1 required functional Sp1 binding sites or the TATA box element of HIV-1 LTR for transactivation, 5'-deletion mutants of the HIV-1 LTR were employed. Plasmids pBS/SalI-L, pBS/SalI-L-SH, and pC6/ORF-1(S), a mammalian expression vector containing ORF-1, all transactivated a deletion mutant of HIV-1 LTR lacking functional Sp1 binding sites (CD-54). These studies demonstrate that transactivation occurred in the absence of Sp1 binding sites and required only a minimal HIV-1 promoter which contains the TATA box element. The specificity of the SalI-L transactivator for HIV-1 LTR was demonstrated by its inability to transactivate the human papillomavirus type 16 or 18 early promoters. The ORF-1 gene was cloned into and expressed from the pET17b bacterial expression vector. Purified ORF-1 protein was obtained by ammonium sulfate precipitation, Mono-S chromatography, and anti-T7. Tag immunoaffinity chromatography. Transactivation of the HIV-1 LTR by ORF-1 protein was demonstrated by electroporation studies in vivo and by transcription studies in vitro. To substantiate the putative biological role of ORF-1, pBS/SalI-L, pBS/SalI-L-SH, and pC6/ORF-1 all reactivated tat-defective HIV-1 provirus from latently infected cells expressing CD4. Thus, the data presented suggest that HHV-6 infection could have a cofactor role in the progression of AIDS.

Direct interaction of human TFIID with the HIV-1 transactivator tat.

The tat gene of the human immunodeficiency virus (HIV) plays a central role in the activation and life cycle of HIV. The tat protein (Tat) specifically transactivates HIV transcription in vivo and in vitro, exerting its effects at the level of transcriptional initiation and elongation. Here we report that Tat binds directly to the basal transcription factor TFIID. The transcriptional activity of HeLa extracts was depleted after chromatography on a Tat affinity column, which specifically retained the polymerase II-specific factor TFIID. Direct interaction of Tat with holo-TFIID, composed of TATA-binding protein (TBP) and associated factors (TAFs), was observed. Tat binds, through amino acids 36-50, directly to the TBP subunit of TFIID. Our results suggest that Tat may transduce upstream or downstream regulatory signals by direct interaction with the basal transcription factor TFIID.

Involvement of transcription factor YB-1 in human T-cell lymphotropic virus type I basal gene expression.

Sequences which control basal human T-cell lymphotropic virus type I (HTLV-I) transcription likely play an important role in initiation and maintenance of virus replication. We previously identified and analyzed a 45-nucleotide sequence (downstream regulatory element 1 [DRE 1]), +195 to +240, at the boundary of the R/U5 region of the long terminal repeat which is required for HTLV-I basal transcription. We identified a protein, p37, which specifically bound to DRE 1. An affinity column fraction, containing p37, stimulated HTLV-I transcription approximately 12-fold in vitro. We now report the identification of a cDNA clone (15B-7), from a Jurkat expression library, that binds specifically to the DRE 1 regulatory sequence. Binding of the cDNA fusion protein, similarly to the results obtained with purified Jurkat protein, was decreased by introduction of site-specific mutations in the DRE 1 regulatory sequence. In vitro transcription and translation of 15B-7 cDNA produced a fusion protein which bound specifically to the HTLV-I +195 to +240 oligonucleotide. The partial cDNA encodes a protein which is homologous to the C-terminal 196 amino acids of the 36-kDa transcription factor, YB-1. Cotransfection of a YB-1 expression plasmid increases HTLV-I basal transcription approximately 14-fold in Jurkat T lymphocytes. On the basis of the molecular weight, DNA-binding characteristics, and in vivo transactivation activity, we suggest that the previously identified DRE 1-binding protein, p37, is YB-1.

Adopted and biological children in the clinic: family, parental and child characteristics.

Adopted children are overrepresented in referrals to mental health facilities. Research has described child symptomatology but has rarely described family characteristics or how adoptive and biological families presenting a child for treatment differ. This study took a systemic approach carrying out a multilevel assessment of families of adopted and biological children presented for treatment with adopted and biological nonclinical comparison groups. The results from this study of 88 parents of 7-17-year-old children suggest that adoptive families have greater social and psychological resources that can be relied on in treatment. However, adopted children are perceived to have more problems and their families are more likely to consider removal of the child as a solution to problems. Therapists' failure to appreciate these unique strengths and vulnerabilities of adoptive families can lead to treatment failure.

Sequences downstream of the RNA initiation site regulate human T-cell lymphotropic virus type I basal gene expression.

Sequences which control basal human T-cell lymphotropic virus type I (HTLV-I) transcription probably play an important role in initiation and maintenance of virus replication. We have identified and analyzed a 45-nucleotide sequence (downstream regulatory element 1 [DRE 1]) at the boundary of the R/U5 region of the long terminal repeat which is required for HTLV-I basal transcription. The basal promoter strength of constructs that contained deletions in the R/U5 region of the HTLV-I long terminal repeat were analyzed by chloramphenicol acetyltransferase assays following transfection of Jurkat T cells. We consistently observed a 10-fold decrease in basal promoter activity when sequences between +202 to +246 were deleted. By reverse transcriptase polymerase chain reaction RNA analysis, we confirmed that the drop in chloramphenicol acetyltransferase activity was paralleled by a decrease in the level of steady-state RNA. DRE 1 did not affect the level of Tax1 transactivation. Using a gel shift assay, we have purified a highly enriched fraction that could specifically bind DRE 1. This DNA affinity column fraction contained four detectable proteins on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis: p37, p50, p60, and p100. The affinity column fraction stimulated HTLV-I transcription approximately 12-fold in vitro. No effect was observed with the human immunodeficiency virus or adenovirus major late promoters. Following renaturation of the proteins isolated from an SDS-containing gel, p37, but not the other protein fractions, was able to specifically bind to DRE 1.

Protein B: a versatile bacterial Fc-binding protein selective for human IgA.

Protein B, a selective bacterial IgA Fc-binding protein isolated from group B streptococci, has been used to quantify fluid phase and immobilized human IgA. Protein B detects both human IgA1 and IgA2 subclasses and is also reactive with secretory IgA. Protein B can be used immobilized to microtiter plates to capture IgA or following biotinylation as a tracer for fluid phase or immobilized human IgA. The studies presented here suggest protein B will prove to be a valuable reagent for quantitative immunochemical procedures involving human IgA antibodies and facilitate a variety of studies of IgA responses in man.

The product of the c-ets-1 proto-oncogene and the related Ets2 protein act as transcriptional activators of the long terminal repeat of human T cell leukemia virus HTLV-1.

The c-ets-1 proto-oncogene and the related c-ets-2 gene encode related nuclear chromatin-associated proteins which bind DNA in vitro. To investigate the possibility that Ets1 and Ets2 are transcriptional activators, we analyzed the ability of these proteins to trans-activate promoter/enhancer sequences in transient co-transfection experiments. A CAT construct driven by the long terminal repeat of the human T cell leukemia virus, HTLV-1 was found to be trans-activated by both Ets1 and Ets2 in NIH3T3 and HeLa cells. The increased levels of CAT activity were paralleled by increased levels of correctly initiated CAT mRNA. Mutant Ets1 proteins unable to accumulate in the nucleus were found to be inactive. An ets-responsive sequence between positions -117 and -160 of the LTR was identified by analyses of a series of 5' deletion mutants of the HTLV-1 LTR and of dimerized versions of specific motifs of the LTR enhancer region. Using a gel shift binding assay, Ets1 was found to bind specifically to an oligonucleotide corresponding to region -117 to -160. This sequence, which also contributes to Tax1 responsiveness of the HTLV-1 LTR, is characterized by the presence of four repeats of a pentanucleotide sequence of the type CC(T/A)CC. Competition experiments show that integrity of repeats 1 and 4 is important for Ets1 binding. These results show that Ets1 and Ets2 are sequence-specific transcriptional activators. In view of the high level expression of Ets1 in lymphoid cells, Ets1 could be part of the transcription complex which mediates the response to Tax1 and the control of HTLV-1 replication. More generally, Ets1 and Ets2 could regulate transcription of cellular genes.