An additional human serine tRNA gene.

In humans, there are about 1,300 tRNA genes in the haploid genome, encoding about 60 different cytoplasmic tRNAs (1). However, only a few of them have been isolated and sequenced. We have cloned human serine tRNA genes for the purpose of studying the structure and genomic organization of a human serine tRNA gene family. We have isolated five different X-phage clones which were hybridized with [5'_32p] labelled human serine tRNAs as probes (2). One of the clones (Xstl9A) contains a 3.1 kb EcoRI fragment which carries two human serine tRNA genes, and the 350 bp EcoRI-Hinfi subfragment (pST19A-2) of the EcoRI fragment was sequenced on the both orientations by dideoxy chain-termination method. The sequence analysis revealed that the gene forms a typical cloverleaf structure with all appropriate conserved bases, and the anticodon sequence is 5'-UGA-3'. The gene does not have any intervening sequences nor does it encode 3'-terminal CCA found in mature tRNAs. Putative transcription termination site of RNA polymerase llI(TTTT) was also found in the 3' flanking region. The nucleotide sequence of this gene is highly homologous to previously sequenced human serine tRNA genes(2, 3, 4, 5) and rat serine tRNA (AGA) gene (6). The sequence variations of the coding regions of human serine tRNA genes are illustrated in Figure 1.