[Activity of polynucleotide phosphorylase in ribosomal fraction of rat liver].

A method of isolating polynucleotidephosphorylase (PNPase) containing polyribosome fraction from rat liver is described. PNPase is found to be bind to RNA in polyribosomes with weak electrostatic bonds which are easily broken down in a weak alkaline medium with ionic strength more than 0.1 beta-22P-labelled ADP, GDP, UDP and CDP are found among the products of endogenous RNA degradation in the fraction of total polyribosomes in the presence of 32P-orthophosphate. A considerable change in the base composition of PNP-degraded RNA is observed at different incubation times of total polyribosomes with 32P-orthophosphate: G+C//A+U ratio increased from 2.3 to 3.1, and purines/pyrimidines ratio-from 0.47 to 1.06 with the increase of the incubation time. Specific activity of PNP in ribosome fractions obtained under ultracentrifugation of total polyribosomes in succrose density gradient (0.3-1.0 M) increased in the direction from the fraction of heavy polysomes to trimers and dimers and then dropped at the region of monomers (80 S particles). The data obtained give no possibility to determine the type of PNP-bound RNA in polyribomes of rat liver.