The gross anatomy of a tRNA gene cluster at region 42A of the D. melanogaster chromosome.

The sequence organization and positions of the tRNA genes in a tRNA gene cluster at chromosomal region 42A of the D. melanogaster (Dm) genome have been studied by recombinant DNA methods. A set of overlapping inserts of Dm DNA cloned in a lambdoid vector and extending in both directions from the Drosophila tRNA gene-bearing fragment of plasmid pCIT12 has been isolated by the procedure of "chromosomal walking." The isolated region has a total length of 94 kb of which a central 46 kb region contains eight tRNAAsn genes, four tRNA2Arg genes, five tRNA2Lys genes and one tRNAIle gene. The genes are irregularly spaced and transcribed from both strands; they occur to some extent in subclusters. Thus this sequence organization is totally different from the tandem repeat organizaiton seen in many 5S rRNA gene clusters of higher eucaryotes and in one Xenopus rRNA gene clusters of higher eucaryotes and in one Xenopus tRNA gene cluster.