[Inhibitors of exonuclease A5].

Over 30 compounds resembling to or being structural elements of the minimal substrate of exonuclease A5 were tested for their ability to inhibit the reaction catalyzed by this nuclease. The compounds containing less than two phosphate groups were shown to possess a low inhibitory activity, if any. CDP, double-stranded DNA and nucleoside-3',5'-diphosphates (pNp) proved to be effective exonuclease A5 inhibitors.

[A mechanism of mononucleotide formation under endonuclease hydrolysis].

It has been shown under poly-A hydrolysis by endonuclease A236 in the presence of large amounts of E. coli phosphatase that the formation of mononucleotides requires the presence of terminal 5'-P in the substrate. Simultaneously, it has been found for endonuclease A236 and nuclease of Serratia marcescens that the products of exhaustive hydrolysis carried out in the presence of excess amounts of phosphatase contain an additional nucleoside residue as compared to the ordinary products of exhaustive hydrolysis, the number of phosphate groups being equal in both cases.

[Some peculiarities of transfer RNAs hydrolysis by exonuclease A5].

Unusual kinetics of the hydrolysis of the baker's yeast total tRNA and tRNA1Val by exonuclease A5 was found (two stages of the reaction; low initial velocity and still lower velocity of the second reaction stage; high Km values). These peculiarities were shown to be due to the three-dimensional structure of the substrate, which makes a large part of the tRNA molecule resistant to the exonuclease A5 attack. The exhaustive tRNA hydrolysis observed in the presence of very large doses of exonuclease A5 may be explained by a slight (less than 1%) endo-RNAase contamination in the exonuclease A5 preparation.

[Nucleases. Biological role].

In the first part of the review (R. I. Tatarskaya, 1976, Mol.

[Isolation of exonuclease A5 preparation free of phosphomonoesterase contamination].

A method is described of the isolation of exonuclease from cultural medium of Actinomyces sp. of coelicolor type, strain 5. The enzyme preparation is practically free from phosphatase activity (the ratio between exonuclease and phosphatase activities is about 10000).