RNA-binding properties of the 63 kDa protein encoded by the triple gene block of poa semilatent hordeivirus.

The 63 kDa '63K' movement protein encoded by the triple gene block of poa semilatent virus (PSLV) comprises the C-terminal NTPase/helicase domain and the N-terminal extension domain, which contains two positively charged sequence motifs, A and B. In this study, the in vitro RNA-binding properties of PSLV 63K and its mutants were analysed. Membrane-immobilized 63K and N-63K (isolated N-terminal extension domain) bound RNA at high NaCl concentrations. In contrast, C-63K (isolated NTPase/helicase domain) was able to bind RNA only at NaCl concentrations of up to 50 mM. In gel-shift assays, C-63K bound RNA to form complexes that were unable to enter an agarose gel, whereas complexes formed by N-63K could enter the gel. Full-length 63K formed both types of complexes. Visualization of the RNA-protein complexes formed by 63K, N-63K and C-63K by atomic force microscopy demonstrated that each complex had a different shape. Collectively, these data indicate that 63K has two distinct RNA-binding activities associated with the NTPase/helicase domain and the N-terminal extension domain. Mutations in either of the positively charged sequence motifs A and B had little effect on the RNA binding of the N-terminal extension domain, whereas mutations in both motifs together inhibited RNA binding. Hybrid viruses with mutations in motifs A and B were able to infect inoculated leaves of Nicotiana benthamiana plants, but were unable to move systemically to uninoculated leaves, suggesting that the RNA-binding activity of the N-terminal extension domain of PSLV 63K is associated with virus long-distance movement.

Parallel-stranded DNA with mixed AT/GC composition: role of trans G.C base pairs in sequence dependent helical stability.

Parallel-stranded (ps) DNAs with mixed AT/GC content comprising G.C pairs in a varying sequence context have been investigated. Oligonucleotides were devised consisting of two 10-nt strands complementary either in a parallel or in an antiparallel orientation and joined via nonnucleotide linkers so as to form 10-bp ps or aps hairpins. A predominance of intramolecular hairpins over intermolecular duplexes was achieved by choice of experimental conditions and verified by fluorescence determinations yielding estimations of rotational relaxation times and fractional base pairing. A multistate mode of ps hairpin melting was revealed by temperature gradient gel electrophoresis (TGGE). The thermal stability of the ps hairpins with mixed AT/GC content depends strongly on the specific sequence in a manner peculiar to the ps double helix. The thermodynamic effects of incorporating trans G.C base pairs into an AT sequence are context-dependent: an isolated G. C base pair destabilizes the duplex whereas a block of > or =2 consecutive G.C base pairs exerts a stabilizing effect. A multistate heterogeneous zipper model for the thermal denaturation of the hairpins was derived and used in a global minimization procedure to compute the thermodynamic parameters of the ps hairpins from experimental melting data. In 0.1 M LiCl at 3 degrees C, the formation of a trans G.C pair in a GG/CC sequence context is approximately 3 kJ mol(-)(1) more favorable than the formation of a trans A.T pair in an AT/TA sequence context. However, GC/AT contacts contribute a substantial unfavorable free energy difference of approximately 2 kJ mol(-)(1). As a consequence, the base composition and fractional distribution of isolated and clustered G.C base pairs determine the overall stability of ps-DNA with mixed AT/GC sequences. Thus, the stability of ps-DNA comprising successive > or =2 G.C base pairs is greater than that of ps-DNA with an alternating AT sequence, whereas increasing the number of AT/GC contacts by isolating G.C base pairs exerts a destabilizing effect on the ps duplex. Molecular modeling of the various helices by force field techniques provides insight into the structural basis for these distinctions.

Gene-specific silencing by expression of parallel complementary RNA in Escherichia coli.

Gene-specific silencing refers to a phenomenon in which expression of an individual gene can be specifically repressed by different mechanisms on the levels of transcription, RNA splicing, transport, degradation in nuclei or cytoplasm, or blocking of translation. In different species gene-specific silencing was observed by expression or injections of antiparallel double-stranded RNA formed by a fragment of mRNA and antisense RNA. Here we show a potent and specific gene silencing in bacteria by expression of RNA, that is complementary in a parallel orientation to Escherichia coli lon mRNA. Moreover, the expression of parallel RNA is more effective at producing interference than expression of antisense RNA corresponding to the same mRNA region. Both effects of interference mediated either by parallel RNA or antiparallel RNA gradually decrease up to the 40th generation. Together with in vitro nuclease protection studies these results indicate that a parallel RNA duplex might be formed in vivo and both types of duplexes, antiparallel or parallel, can induce gene-specific silencing by similar mechanisms.

[Generation of Kruppel phenocopies by injecting into Drosophila embryos RNA complementary to mRNA in parallel orientation]. / Poluchenie fenokopii Kruppel pri in''ektsiiakh v émbriony drozofily RNK, komplementarnoi mRNK v parallel'nom napravlenii.

RNA preparations synthesized in vitro were used to study the influence of RNA interference on the Kruppel gene activity in Drosophila embryos. RNA complementary in parallel orientation to the mRNA fragment proved to induce the development of Kruppel phenocopies. The data obtained indicate that mechanisms of specific regulation of gene activity exist in Drosophila cells, which are sensitive to the formation of both parallel and antiparallel RNA-RNA duplexes that include mRNA of the corresponding gene.

Advanced method for oligonucleotide deprotection.

A new procedure for rapid deprotection of synthetic oligodeoxynucleotides has been developed. While all known deprotection methods require purification to remove the residual protective groups (e.g. benzamide) and insoluble silicates, the new procedure based on the use of an ammonia-free reagent mixture allows one to avoid the additional purification steps. The method can be applied to deprotect the oligodeoxynucleotides synthesized by using the standard protected nucleoside phosphoramidites dG(iBu), dC(Bz)and dA(Bz).

DNA sequence recognition by bis-linked netropsin and distamycin derivatives.

We studied the interaction of cis-diammine Pt(II)-bridged bis-netropsin, cis-diammine Pt(II)-bridged bis-distamycin and oligomethylene-bridged bis-netropsin with synthetic DNA fragments containing pseudosymmetrical AT-rich nucleotide sequences and compared it with the interaction of the parent compounds netropsin and distamycin A. For fragments containing multiple blocks of (AIT)4 and (T/A)4 separated by zero, one, two and three GC-base pairs, DNase I footprinting and CD spectroscopy studies reveal that 5'-TTTTAAAA-3' is the strongest affinity binding site for cis-diammine Pt(II)-bridged bis-netropsin and bis-distamycin. They both bind less strongly to a DNA region containing the sequence 5'-AAAATTTT-3'. Netropsin, distamycin A and oligomethylene-bridged bis-netropsin exhibit far less sequence discrimination.

Forum domain in Drosophila melanogaster cut locus possesses looped domains inside.

We have studied the relationship between chromosomal forum domains and looped domains in the cut locus of Drosophila melanogaster . Forum domains were earlier detected by separation in pulsed-field gels of 50-150 kb chromosomal DNA fragments obtained after spontaneous non-random degradation of chromosomes. We have localized the boundary region where cleavage sites are scattered between two forum domains in the regulatory region of the cut locus. We have sequenced a 13 kb region spanning few kilobases from distal domain, the boundary region and part of the proximal forum domain where several scaffold associated regions (SARs) were observed. We conclude that forum domains and looped domains are physically different types of domains and belong to different levels of organization in eukaryotic chromosomes. The boundary region between the neighboring forum domains in the cut locus possesses the Doc element insertion and a micro-satellite stretch and thus might remind a small island of heterochromatin and correspond to so-called intercalary heterochromatin that is known to be located in the 7B1-2 band where the major part of the cut locus is reside.

The role of phosphorylation of DNA-binding proteins in regulation of transcription of the human c-myc gene.

The goal of the present study was to identify transcriptional factors, to determine their specificity toward nucleotide sequences of binding sites, and to elucidate their regulatory effects on transcription of the human c-myc oncogene. Three novel phosphorylated proteins (transcriptional factors) participating in the regulation of transcription of the c-myc gene have been identified, and the following data have been obtained. A) The binding of the regulatory phosphoproteins activates in vitro transcription of the human c-myc gene. B) The recognition sites for the three discovered DNA-binding proteins, i.e., p70, p35, and p23, have been mapped in the c-myc promoter. C) The site-specific mutagenesis of p70 binding sites of the c-myc gene has been performed and the recognition sequence has been identified. The mutagenesis was carried out using the PCR technique using oligonucleotide primers with mismatches in the p70 binding site. The wild-type sequence GGGAAAAGAAAAAA showed the highest affinity toward p70, while the mutant sequence GAAAAtGAcAct exhibited a lack of affinity for the protein. The participation of p70 and other phosphorylated transcriptional factors in regulation of the human c-myc gene expression is discussed.

The formation of parallel RNA-RNA duplexes in vitro.

Over the years the structural properties of nucleic acids have been of interest, providing data that may be of importance for DNA and RNA organization and function in the cell. We have attempted to look for the formation of parallel RNA-RNA duplexes in vitro. RNA molecules comprising complementary in the same polarity alternating stretches of A and U of increasing length were enzymatically synthesized and annealed in physiological conditions. The fractionation in the denaturing polyacrylamide gels revealed the formation of two types of full-length parallel RNase A-stable duplexes established either by A-U or by A-A and U-U self pairs. These results suggest novel structural properties of versatile RNA molecules that potentially may be realized in vivo.

DNA mobility in crystals of a nonspecific lambda cro/DNA complex.

DNA location in the crystal of the nonspecific lambda cro/(GT)4.(AC)4 complex has been studied by the isomorphous replacement method using iodinated and brominated oligonucleotides. The results of the search for heavy atom positions combined with previously obtained molecular replacement data suggest that the DNA octamer occupies two overlapping positions, each of the two duplexes (GTGTGTGT).(ACACACAC) belonging to the same imaginary longer double helix and differing only in the shift by two base pairs along the common sugar-phosphate backbone. In the crystals of the heavy atom derivatives different orientations of the DNA octamer are observed as well. It seems reasonable that the DNA mobility of both kinds might be a common feature of crystals of nonspecific repressor/DNA complexes.

Mutants of T7 RNA polymerase that are able to synthesize both RNA and DNA.

A mutant T7 RNA polymerase (T7 RNAP) having two amino-acid substitutions (Y639F and S641A) is altered in its specificity towards nucleotide substrates, but is not affected in the specificity of its interaction with promoter and terminator sequences. The mutant enzyme gains the ability to utilize dNTPs and catalyze RNA and DNA synthesis from circular supercoiled plasmid DNA. DNA synthesis can also be initiated from a single stranded template using a DNA primer. Another T7 RNAP mutant having only the single substitution S641A loses RNA polymerase activity but is able to synthesize DNA.

Poly(A) addition site mapping and polyadenylation signal analysis in a plant circovirus replication-related gene.

The transcripts of a genomic component of coconut foliar decay virus (CFDV), a plant circovirus with a single-stranded DNA genome, were characterized by sequencing the 3' termini of the respective cDNA clones. It was shown that transcription of the putative replication-related gene terminated at one major site (six bases downstream of the termination codon) in electroporated barley mesophyll protoplasts and that the resulting transcripts were polyadenylated. A deletion downstream of the AATAAA sequence including the poly(A) addition site did not inhibit polyadenylation signal activity but altered the distance between the polyadenylation signal and the polyadenylation site. However, deletion of the sequences upstream of the AATAAA stretch resulted in inhibition of the polyadenylation in this region. These observations and the finding of a silent CFDV AATAAA sequence downstream of the active poly(A) signal confirm the role of the upstream elements in processing of RNA transcripts in plants.

Targeted mutagenesis identifies Asp-569 as a catalytically critical residue in T7 RNA polymerase.

In order to look more closely at a well-conserved region in T7 RNA polymerase (T7 RNAP) containing, as shown earlier, the functionally essential residues Pro-563 and Tyr-571, we used targeted mutagenesis to change those residues within this region that are invariant in all single-subunit RNA polymerases, and characterized the mutant enzymes in vitro. The most interesting finding of this study was the crucial importance of the acidic group of Asp-569. In addition, we have shown that the phenolic ring is the most significant functional group of Tyr-571, with the hydroxy group also contributing to promoter binding.