[Modification of Escherichia coli RNA polymerase by diethylpyrocarbonate. II. Binding and unwinding of double-stranded DNA]. / Mosidikatsiia RNK-polimerazy Escherchia coli dietilpirokarbonatom. II. sviazyvanie i destabilizatsiia dvoinoi spirali DNK.

E. coli DNA dependent RNA polymerase was modified by diethylpyrocarbonate. Binding to a double-stranded DNA and unwinding of the DNA at the enzyme binding site by the modified enzyme were examined. It was found that RNA polymerase reversibly lost the ability to unwind DNA helix as well as the RNA synthetic activity when 9 to 11 histidyl residues of the enzyme were modified. In addition ot modification of the most reactive sulfhydryl or amino groups of the enzyme accompanying histidyl residues modification results in irreversible decrease of the salt concentration which is necessary to remove the enzyme from DNA cellulose column. Further modification of the less reactive sulfhydryl or amino groups leads to irreversible loss of the DNA binding ability and to the enzyme structure alteration.

[Use of the reaction product of beta-alanine and formaldehyde in the kinetic method of determining defects in secondary structure]. / Ispol'zovanie produkta vzaimodeistviia beta-alanina s formal'degidom v kineticheskom metode opredeleniia defektov vtorichnoi struktury DNK.

It is shown that the kinetics of DNA despiralization in the presence of beta-alanine--formaldehyde reaction product (beta-ALA-FORM) can be described in terms of theory of DNA despiralisation by "slowly reacting agents". Conditions are determined in which beta-ALA-FORM product can be used to establish the concentration of defects in DNA secondary structure. Possible advantages are discussed of using the new agent in the kinetic method of determining DNA defects as compared to formaldehyde, in particular in analysis of DNA complexes with proteins. The data obtained throw some light on the nature of the interaction between beta-alanine and formaldehyde in slightly acidic solutions and with the excess of aminoacid.

[Intramolecular double-stranded helices of polyadenylic acid and their possible biological significance].

Under protonation of the single-stranded polyadenylic acid so called "frozen" form arises simultaneously with formation of two double-stranded forms. It has been shown that a portion of the polyadenylic acid "frozen" form increases with the size of poly(A) and ionic strength of solution, i. e. with an increase of polymer chain flexibility. These findings may be considered as evidences in favor of our earlier supposition on poly(A) ability to fold with formation of intramolecular double-stranded helices. Ten years ago we also proposed a hypothesis that such double-stranded helices can be formed in poly(A) tracts of cellular RNAs and they can participate in several biological processes. An analysis of literature data published later evidences for the hypothesis adequacy and shows that it still remains urgent.

[Is it reality that the endonuclease that cleaves pre-mRNA on polyadenylation has not been discovered?]. / Deistvitel'no li do sikh por ne obnaruzhena éndonucleaza, rasshchepliaiushchaia pro-mRNK v reaktsii poliadenilirovaniia?

Specific cleavage of transcript by a complex of multisubunit proteins is the first stage of polyadenylation of eukaryotic pre-mRNAs. The main participant of this reaction--endonuclease--is not discovered yet. However it is known that proteins CPSF-30 (mammalian) and Yth 1p (yeast) are homologues of the drosofila protein clipper (CLP), which displays endoribonucleolytic activity. In the N-terminal region all three proteins contain five copies of CCCH zinc finger motif that are associated with nucleolytic activity in the case of CLP. Literature data on the three above-mentioned proteins has been analysed. The results of these works do not contradict the hypothesis that exactly CPSF-30 and its homologues are the actual nucleases that cleave pre-mRNA in the process of polyadenylation.

[Molecular mechanisms of coupling processes of transcription termination and polyadenylation of pro-mRNA]. / Molekuliarnye mekhanizmy sopriazheniia protsessov terminatsii transkriptsii i poliadenilirovaniia pro-mRNK.

The recent literature data devoted to coordination of the processes of the transcription termination and polyadenylation have been analyzed. The model of coupling of these processes synthesizing the available conceptions is proposed. The effective transcription termination occurs under simultaneous interactions of RNA polymerase (Pol II) both with the signal element of DNA (terminator or enhancer) and the transcript polyadenylation site. The unique C-terminal domain (CTD) of the largest enzyme subunit contacts pre-mRNA. The cleavage factors are associated with this domain. Pol II is an essential cofactor in the cleavage reaction. The mechanism of this reaction influence on the termination transcription is unknown but the cleavage is accompanied by degradation of the 3' end part of the transcript. The RNA release from Pol II induces destabilization of the contact between the enzyme and the DNA duplex immediately after the transcription bubble, which promotes release Pol II from the template.