Changes of tRNA population during compensatory cell proliferation: differential expression of methionine-tRNA species.

Changes of tRNA species, as both relative percentage of total tRNA and absolute concentration, occur during liver cell proliferation induced by partial hepatectomy. Transfer RNAs which are abundant under quiescence are found to decrease during hepatocyte proliferation, and vice versa. One consequence of these changes is the differential expression of methionine-isoaccepting tRNA species. Initiator tRNA(Met) is present in scarce amounts under quiescent conditions and increases during cell-cycle progression. Elongator tRNA(Met) shows the opposite behavior. Both the quantitative and qualitative tRNA changes return to control levels as the liver returns to resting conditions. These changes might have mechanistic implications in modulating the protein synthesis required by cell proliferation. Moreover, the increase of initiator tRNA(Met) species might be necessary to translate protooncogene, growth factor, and receptor mRNAs, the translation of which is hindered by inhibitory AUG triplets upstream from the coding sequence. Thus the tRNA changes described herein could be involved in regulating translation of transcripts encoding cell-cycle associated proteins.