Association of aminoacyl transferase II with ribosomes of intact HeLa cells during amino acid deprivation.

The ADP ribosylation in vifro of aminoacyl transferase II, catalyzed by diphtheria toxin, was used to determine the subcellular location of transferase II in extracts obtained from intact HeLa cells incubated under a variety of conditions. Very little transferase II was found associated with either heavy or light polyribosomes, most of the ribosome-associated enzyme being bound to monoribosomes. Incubation conditions of cells which increased the amount of monoribosomes, such as amino acid deprivation and puromycin inhibition of protein synthesis, caused an increased binding of the enzyme to monoribosomes compared to controls. Transferase II, accumulated on monoribosomes as a result of amino acid deprivation, was rapidly released into the cytoplasm upon restoration of protein synthesis. The free 74 S monoribosomes contained almost all of the ribosome-bound aminoacyl transferase II; only traces were found associated with nascent 60 S and 40 S ribosomal subunits.