COMPLEX ORGANIZATION OF THE 5'-END OF THE HUMAN GLYCINE TRANSFER-RNA SYNTHETASE GENE

Glycine tRNA synthetase (glyRS) catalyses the addition of tie amino ac id glycine to its cognate tRNA molecules. In the silk moth worm Bombyx mori, this gene is subject to complex transcriptional regulation beca use of the predominance of glycine in silk. In vertebrates, glycine is a major constituent of collagen but there have been no studies of gly RS regulation. In this study we have isolated and mapped a genomic clo ne containing the 5'-end of glyRS, Primer extension studies identified only one transcriptional start point (TSP) in three different cell li nes. Expression of the transcript identified may be regulated translat ionally because it contains five potential initiation codons, three of which are in good context for initiation. The most 3' of the potentia l initiation codons has previously been predicted to be the initiating codon for cytoplasmic glyRS. Two of the upstream codons are in-frame with this codon, and both are predicted to extend the N-terminus of gl yRS to include a mitochondrial targeting sequence. Sequencing of genom ic DNA surrounding the TSP showed features common to the promoters of housekeeping genes, as well as a canonical TATA box at the unusual pos ition of +9, Surprisingly, remoter activity in vitro was not specified by a 1.9 kb genomic fragment containing the TSP and TATA box, but by a contiguous 0.4 kb fragment immediately downstream. These studies sug gest that the transcription of glyRS from a single start point require s downstream promoter elements. (C) 1998 Elsevier Science B.V.