Analysis of a drosophila tRNA gene cluster

Abstract

The arrangement and the nucleotide sequences of the tRNA genes in a 9.3 kb fragment of Drosophila DNA have been determined. This fragment, cloned in Col E1 to form the plasmid pCIT12 (Yen et al. 1977), contains eight tRNA genes. These are irregularly spaced within the DNA and encode a single tRNA 2 Arg, three tRNA Asn, one tRNA IIe and three tRNA 2 Lys. Each DNA strand contains the coding sequences for several tRNA genes, and the transcription direction differs for the various genes of the same isoacceptor. We propose that the inverted repeat secondary structure features observed by electron microscopy in the single-stranded DNA (Yen et al. 1977) are formed by tRNA genes. This finding explains the difficulty in detecting all the tRNA genes by hybridization of DNA with radioactive tRNA. These Drosophila tRNA genes do not contain intervening sequences; nor do they encode C-C-A, the 3′ terminal sequence of mature tRNA. Computer analysis of the DNA sequences revealed a conserved undecanucleotide sequence found only in the 5′ flanking regions of the three tRNA Lys genes; no sequence common to all tRNA gene regions in pCIT12 was detected. pCIT12 did not contain any homology to the “consensus sequence” found in the 5′ flanking regions of Xenopus 5S genes (Korn and Brown 1978) or to the transcription control region found within those genes (Sakonju, Begenhagen and Brown 1980).