Nucleotide sequence and transcription of a human tRNA gene cluster with four genes

Abstract

A bacteriophage λ clone containing a 20-kb human DNA segment was isolated and found to harbor a cluster of four tRNA genes. An 8.2-kb HindIII subfragment encompassing the genes was cloned into pBR322 for restriction mapping and DNA sequence analysis. The genes were found to be arranged as two tandem pairs, separated by 3 kb. A proline tRNA AGG gene is separated from a leucine trna aag gene by a 724-bp intergenic region in the first pair, and a second proline tRNA AGG gene is 316 bp from a threonine tRNA UGU gene in the second pair, with the leucine tRNA gene being of opposite polarity to the other three genes. A putative Alu-like element was found to occur within a 2.0-kb DNA fragment, at least 0.7 kb from the tRNA gene cluster. The coding sequences of the two proline iRNA AGG genes are identical. The coding regions of all four tRNA genes contain consensus internal split promoter sequences and do not have intervening sequences nor the CCA trinucleotide found in mature tRNAs. The 3'-flanking regions of these four tRNA genes have normal RNA polymerase III termination sites of at least four consecutive T nucleotides. No apparent homologies occur between the 5'-flanking regions of these genes. All four tRNA genes are accurately transcribed in an in vitro HeLa cell-free system, and the RNase T 1 fingerprints of the mature-sized tRNA transcripts were found to be consistent with the DNA sequences of the genes.