Structure and expression of several bean (: relevance to the process of tRNA import into plant mitochondriaPhaseolus vulgaris: relevance to the process of tRNA import into plant mitochondria) nuclear transfer RNA genes: relevance to the process of tRNA import into plant mitochondria

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Abstract

Bean nuclear genes for tRNAPro, tRNAThrand tRNALeu were isolated. Expression of the tRNAPro genes was demonstrated in vivo and sequence analysis suggested amplification of the tRNAPro gene copy number through duplication of a gene cluster at the same locus of the bean genome. The two tRNAThr genes isolated were actively transcribed and their transcripts processed in a HeLa cell system. In vivo expression tests of these genes and aminoacylation assays of the corresponding in vitro transcripts showed the presence of identity determinants in the anticodon of plant tRNAThr. The tRNALeu gene was not expressed due to deviation from the consensus in the internal B-box promoter. The same sequence deviation also prevented aminoacylation of the corresponding in vitro transcript. This tRNALeu however exists in plants and is synthesized from another gene with a consensus B-box promoter. Plant mitochondria import from the cytosol a number of nucleus-encoded tRNAs, including tRNALeu and tRNAThr. From the available sequence data, we could not identify any conserved structural motif characteristic for the nucleus-encoded tRNAs imported into plant mitochondria, either in the tRNAs, or in the gene flanking sequences. These results suggest that recognition of tRNAs for import is idiosyncratic and likely to depend on protein/RNA interactions that are specific to each tRNA or each isoacceptor group.

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