ANALYSIS OF STRUCTURE OF T4-BACTERIOPHAGE-MODIFIED VALYL-TRANSFER-RNA SYNTHETASE BY LIMITED PROTEOLYSIS AND ISOELECTRIC-FOCUSING

  • 1 January 1977
    • journal article
    • research article
    • Vol. 252  (19) , 6646-6650
Abstract
The new form of valyl-tRNA synthetase (EC 6.1.1.9) that appeared immediately after infection of Escherichia coli with bacteriophage T4 was purified and subjected to mild proteolysis using 5 different proteases. The inactivation of aminoacylation activity was both more extensive and rapid than that obtained with valyl-tRNA synthetase purified from uninfected E. coli. The addition of bulk tRNA from E. coli B protected the phage-specific form of valyl-tRNA synthetase from proteolysis, but ATP and valine did not exhibit a similar protective effect. The characteristic property of phage-modified valyl-tRNA synthetase, resistance to denaturation by 4 M urea, remained unaffected during treatment with trypsin. This suggested that the phage-specific factor .tau., known to be associated with the synthetase in phage-infected cells, was protected from proteolysis in the synthetase.cntdot..tau. complex. Comparison by isoelectric focusing of normal valyl-tRNA synthetase, the phage-specific form of this enzyme, and phage enzyme from which .tau. was removed, revealed no differences in the isoelectric points of these 3 molecules. Based on these results a model was drawn for the structural changes occurring in valyl-tRNA synthetase after association with the phage factor .tau.