NUCLEOTIDE-SEQUENCES OF NUCLEAR TRNA(CYS) GENES FROM NICOTIANA AND ARABIDOPSIS AND EXPRESSION IN HELA-CELL EXTRACT

We have recently characterized Nicotiana cytoplasmic (cyt) tRNA(GCA)(C ys) as a novel UGA suppressor tRNA. Here we have isolated its correspo nding (NtC1) and a variant (NtC2) gene from a genomic library of Nicot iana rustica. Both tRNA(Cys) genes are efficiently transcribed in HeLa cell nuclear extract and yield mature cyt tRNAs(Cys). Sequence analys is of the upstream region of the RAD51 single-copy gene of the Arabido psis thaliana genome revealed a cluster of three tRNA(Cys) genes which have the same polarity and comprise highly similar flanking sequences . Of the three Arabidopsis tRNA(Cys) genes only one (i.e. AtC2) appear s to code for a functional gene which exhibits an almost identical nuc leotide sequence to NtC1. These are the first sequenced nuclear tDNAs( Cys) Of plant origin.