Abstract
tRNA pyrophosphorylase was partially purified from Escherichia coli MRE 600 cells. Upon chromatography on a DEAE‐cellulose column, two enzymatic activity peaks were partially resolved. Gel filtration indicated a molecular weight of approx. 42000 dalton for both. Some general properties are reported. The only consistent difference between the two enzyme fractions was that the first incorporated more AMP‐residues for a given tRNA preparation, as if the second has a more restricted specificity with respect to the acceptor tRNA molecules in the adenylation reaction.Partial degradation of tRNA by combined digestion with ribonuclease T1 and spleen exo‐nuclease indicated a rapid removal of approx. 16 nucleotides per tRNA molecule, presumably from more exposed regions. The amino acid acceptor activity was more sensitive to this nuclease pretreatment than the 3′‐terminal adenylic acid acceptor activity. Direct analysis showed that RNA fragments of chain length approx. 40 and even 10 were still functional in accepting terminal adenylic acid.
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