General and specific effects of amino acid starvation on the formation of undermodified Escherichia coli phenylalanine tRNA.

The heterogeneity of undermodified phenylalanine tRNA produced in relaxed control E. coli during amino acid starvation was investigated. Examination of the RPC-5 elution profiles of tRNAPhe prepared from non-starved cells and cells starved of a variety of amino acids, including some known to be involved in the formation of modified bases revealed that: (1) only one species of fully modified tRNAPhe appears to occur in cells grown in enriched medium; (2) at least two chromatographically unique isoacceptor species are observed in addition to the normal tRNAPhe in starved cells; (3) the unique, undermodified species of tRNAPhe from leucine-starved cells, known to be deficient in dihydrouridine, pseudouridine, 2-thiomethyl-N6-(delta2-isopentenyl) adenosine and 3-(3-amino-3-carboxypropyl) uridine, co-elute with the unique species produced in cells starved of histidine or arginine or treated with puromycin or chloramphenicol; (4) additional unique species of tRNAPhe can be detected in methyl- and sulfur-deficient tRNA from methionine- and cysteine-starved cells; (5) analysis of phenoxyacetylated tRNA revealed that the chromatographically unique and normal species from starved cells contain subspecies deficient in 3-(3-amino-3-carboxypropyl) uridine; and (6) using phenoxyacetylation as a means of effecting the resolution of undermodified subspecies, a total of at least ten chromatographically unique subspecies of rRNAPhe were detected in an organism that appears to posses only one gene for tRNAPhe. Taken together, the results support the view that there are both general and specific effects of amino acid starvation on the post-transcriptional modification of tRNA.