Modified DNA fragments specifically and irreversibly bind transcription factor NF-kappaB in lysates of human tumor cells.

Covalent binding of a synthetic DNA fragment with eukaryotic transcription factor NF-kappaB has been studied in lysates of human colon carcinoma HCT-116 cells. For binding we used 32P-labeled 17/19 bp nucleotide DNA duplex containing an NF-kappaB recognition site (kappaB-site) in which one of internucleotide phosphate groups was replaced by a chemically active trisubstituted pyrophosphate group. Using gel electrophoresis under denaturing conditions (Laemmli electrophoresis) followed by immunoblotting revealed selective irreversible binding of 32P-labeled DNA duplex with NF-kappaB in lysates of tumor cells in the presence of other cell components. Experiment on delivery of this DNA duplex containing rhodamine at 3 -end of the modified chain in an intact cell revealed that rhodamine-labeled DNA penetrated through the plasma membrane of tumor cells without any additional delivery systems. Using fluorescent microscopy, we found that the rhodamine-labeled DNA is initially localized in the cytoplasm. Confocal laser scanning microscopy revealed that subsequent treatment of the cells with TNF-alpha promoted partial translocation of the DNA reagent into the nucleus.

Probing contacts of phosphate groups of oligonucleotides from the non-template strand of lac UV5 promoter with E. coli RNA polymerase using regioselective cross-linking.

Contacts of phosphate groups at positions -12, -15, and -18 in relation to the transcription initiation site in the non-template strand of lac UV5 promoter with lysines or histidines of E. coli RNA polymerase in the open complex model were studied. A number of synthetic oligonucleotides from the -10-area of the non-template strand containing activated 5'-terminal phosphate group were cross-linked with holo- or core-enzyme of RNA polymerase. 5'-N-Hydroxybenzotriazole phosphodiesters of oligonucleotides were used as phosphate activated derivatives. They are capable of phosphorylating amino groups of lysines and histidines in the enzyme molecule that are brought into proximity with activated phosphate in the complex, resulting in the formation of a covalent bond between the oligonucleotide and the protein. The analysis of the products of cross-linking allowed the protein subunit and the amino acid residue taking part in the formation of the covalent bond for each oligonucleotide to be identified. It was found that all oligonucleotides from the non-template strand of promoter in the complex with the holo-enzyme are bound with the sigma70-subunit. When analyzing the products of partial cleavage of the complexes cross-linked at cysteines and methionines using SDS-PAGE, it was shown that phosphate at position -12 made contacts with His180 or His242 of the sigma70-subunit, the reactive amino acid residue being located between the first and second conservative regions. Phosphate at position -15 is located near lysines from two different areas--between Met413 and Met456 (regions 2.3 and 2.4) and between Met470 and Met507 (region 3.1). Phosphate at position -18 makes preferential contacts with a lysine situated between Met470 and Met507 (region 3.1). Based on the analysis of contacts of phosphate groups and the structure of the isolated sigma70-subunit established previously, a scheme of the mutual arrangement of the oligonucleotide and the sigma70-subunit possessed by the holo-enzyme has been proposed.

RNA recognition and regulation of HIV-1 gene expression by viral factor Tat.

Viral transcription factor Tat is a small nuclear protein containing a large number of basic amino acids. The tat gene consists of two exons but only the first encoding 72-amino acid polypeptide is necessary for protein activity. Since the second exon is poorly conservative the total number of amino acids among Tat proteins from different strains of HIV-1 varies from 86 to 130. Tat protein acts as trans-activator of HIV genome transcription. It is absolutely required for viral functioning. Tat increases processivity of RNA-polymerase II by abolition of transcription blockade, which appears after polycondensation of the first 60-70 nucleotides of either HIV mRNA, i.e., it acts as antiterminator. For manifestation of its activity Tat specifically binds to the double stranded RNA fragment called TAR which is located at the 5'-terminus of all HIV mRNAs. The TAR structure contains a hairpin and a side loop. The Tat-binding region includes only a site of the loop; manifestation of Tat activity in vivo requires the full TAR and additional cellular co-factors.

Design of new reagents on the base of DNA duplexes for irreversible inhibition of transcription factor NF-kappa B.

The main purpose of the present work is to search for the optimal design of a DNA duplex containing an active group for crosslinking and irreversible inhibition of the transcription factor NF-kappa B. Modified DNA duplexes with an identical nucleotide sequence but different internucleotide phosphates replaced by the trisubstituted pyrophosphate internucleotide group were synthesized. Crosslinking of the human NF-kappa B p50 subunit with the modified DNA duplexes was carried out. It was shown that only four modified duplexes crosslinked with the NF-kappa B p50 subunit. The specificity of these reactions was confirmed. A position of the phosphate in the NF-kappa B recognition site was found where replacement on the active trisubstituted pyrophosphate group resulted in a 50% yield of crosslinking. The fact that DNA duplexes containing the trisubstituted pyrophosphate group specifically react with the NF-kappa B p50 subunit in the Escherichia coli total lysate supports the idea that such modified DNA can be used as high specific inhibitors for DNA-recognizing proteins.

Chemical cross-linking of the human immunodeficiency virus type 1 Tat protein to synthetic models of the RNA recognition sequence TAR containing site-specific trisubstituted pyrophosphate analogues.

A chemical ligation procedure has been developed for the synthesis of oligoribonucleotides carrying a trisubstituted pyrophosphate (tsp) linkage in place of a single phosphodiester. Good yields of tsp were obtained when a single 2'-deoxynucleoside 5' to the tsp was used in the ligation reaction. A tsp linkage was found to be reasonably stable to hydrolysis but cleaved by treatment with ethylenediamine or lysine to give phosphoamidate adducts. A model human immunodeficiency virus type 1 (HIV-1) TAR RNA duplex containing an activated tsp was able to bind to HIV-1 Tat protein with only 3-fold reduced affinity and to a Tat peptide (residues 37-72) with identical affinity compared to that of an unmodified duplex. Tsps incorporated at sites previously identified as being in close proximity to Tat protein were able to cross-link to Tat peptide (37-72) to form a covalent phosphoamidate conjugate. Endopeptidase cleavage followed by MALDI-TOF (matrix-assisted laser desorption ionization time of flight) mass spectrometric analysis provided strong evidence that a TAR duplex containing a tsp replacing the phosphate at 38-39 had reacted specifically with Lys51 in the basic region of Tat peptide (37-72). The new chemical cross-linking method may be generally useful for identifying lysines in close proximity to phosphates in basic RNA-binding domains of proteins.

Oligonucleotide circularization by template-directed chemical ligation.

An efficient method for producing the covalent closure of oligonucleotides on complementary templates by the action of BrCN was developed. A rational design of linear precursor oligonucleotides was studied, and the effect of factors such as oligonucleotide concentration and oligomer-template length ratio was evaluated. The efficiency of circularization was shown to correlate well with the secondary structure of the precursor oligomer (as predicted by a simple computer analysis), hairpin-like structures bearing free termini clearly favouring the circularization reaction. A novel idea, consisting of the incorporation of non-nucleotide insertions in the precursor oligomer (namely, 1,2-dideoxy-D-ribofuranose residues), may render this method universal and highly effective. An original set of assays was developed to confirm the circular structure of the covalently closed oligonucleotides.