No abstract

Activity in ~he presenc~ of L-v~ne methy] ease, a~fl of L-3-arn~no-4-me~hylp~n1~.~-2-one (rne~yLk,et.~ne) WaS ~ea~ured in the ~am~ way. inhibitionThe ra~,e of ~rever~ib]e kr--~,a'b~-~fon was f~owed by assaying ~e~tty ,(as in 2~.) :an s~anp]e~ at diff~ren~ time~ zfie:r mixing enzyme and ~ ~uh~:bitcr. The ~bitor~, ch]or,orneihyLketones, L-valhae mad L-aspaztme aua]ogUes were incubated w~t~ enzyme ira 0.05 ~M K-phosphate . buffer, pH 7.5 at 25~C. The kine dc constants of 5,~bAbi-don were de;retained v,5 ~th a ] O.0-foid concenlradon ex~.ess of ]nh~bitox o~er e~az3cme. purified beef liver valyl-tRNA syn~et,'~e was oblzSn 2Ao Test for pos~ble reae~q~arion by he p~:o~edure ha ~7] with naoditSca~tioJ~s t,o be " Enzyme (3 n~g/an])was 5a~:mabmed for 5 h~-Lu ~lhe descr~bed ,~lsewhe~.-The preparation eontained ~raeez prose-~c,e o~ 5 X-a:0 -4 aM ~h]0r0rnOllaytke~one or:..~ethyi ofsome other synthetasez anfl.!some olheI pxo~e.ins, .ketone a~ in 2,3, A]iquots were :ddluled 100-fold and

Ten new derivatives of the antibiotic rifamycin with variable side chains at position 3 were synthesized. The inhibitory activity of these derivatives against DNA-polymerases isolated from avian myeloblastosis virus, E. coli and calf thymus were studied at various conditions. 3-(2,4,6-trinitrophenylhydrazone-(methyl) rifamycin SV is a strong inhibitor for all the polymerases tested and belongs to the C class inhibitors of reverse transcriptase. 3-(monoallylhydrazone-(methyl) rifamycin SV possesses a selective action on polymerases: at 0.1 mg/ml concentration it almost completely inhibits the reverse transcriptase and less than half of the bacterial and eukaryotic enzymes. A drug is found which strongly inhibits the DNA-polymerases from E. coli and calf thymus and weakly the viral enzyme. The inhibitory effect on reverse transcriptase is independent of the choice of template-primer; it could be overcome by the addition of excess enzyme but not of excess template-primer; the inhibition could be completely reversed by dilution of the drug-enzyme mixture. From Lineweaver-Burk analysis, the inhibition is noncompetitive with respect to the template-primer and, thus the drugs bind to the site different from the active site for the template-primer. From protective action of the template-primer and other data it might be suggested that the rifamycin derivatives act at an early step(s) in DNA synthesis catalyzed by reverse transcriptase. The obtained data are in agreement with the results for other derivatives of rifamycin SV described in literature.

No abstract

DNA synthesis catalysed by RNA-directed DNA-polymerase (reverse transcriptase) was found to proceed on the RNA template of an MS2 phage in the presence of heteropolymeric synthetic octa- and nonadeoxyribonucleotide primers complementary to the intercistronic region (coat protein binding site) and the region of the coat protein cistron, respectively. The product of synthesis consists of discrete DNA fractions of different length, including transcripts longer than 1,000 nucleotides. The coat protein inhibits DNA synthesis if it is initiated at its binding site, but has no effect on DNA synthesis initiated at the coat protein cistron. It has been suggested that, in this system, the initiation of DNA synthesis by synthetic primers is topographically specific. The MS2 coat protein binding site (an RNA fragment of 59 nucleotides) serves as a template for polydeoxyribonucleotide synthesis in the presence of octanucleotide primer and reverse transcriptase. The product of synthesis is homogenous and its length corresponds to the length of the template. The effective and complete copying of the fragment having a distinct secondary structure proves that the secondary structure does not interfere, in principle, with RNA being a template in the system of reverse transcription.