Abstract
A Met‐tRNA deacylase has been partially purified from the 0.5 M KCI wash of rat liver microsomes. In preparative sucrose gradients, the active component sediments as a single band at about 6 S, corresponding to an estimated molecular weight of 1.7 × 105. The deacylase is specific for Met‐tRNA, without discriminating between Met‐tRNAf and Met‐tRNAm. Met‐tRNAf bound to the initiation factor IF‐MP in the ternary complex, IF‐MP. GTP. Met‐tRNAf, or to initiation‐factor‐dependent, complexes with 40‐S subunits or 80‐S ribosomes, is protected against deacylation. However, in the course of the initiation‐factor‐dependent joining of the 40‐S subunit complex to 60‐S ribosomal subunits, the bound Met‐tRNAf is exposed to added deacylase. Under these conditions, deacylation is inhibited by GTP. The tRNAMetf remains bound and accumulates on the 80‐S ribosomes.

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