A DROSOPHILA HSP70 GENE CONTAINS LONG, ANTIPARALLEL, COUPLED OPEN READING FRAMES (LAG ORFS) CONSERVED IN HOMOLOGOUS LOCI

A clone isolated from a Drosophila auraria heat-shock cDNA library pre sents two long, antiparallel, coupled (LAC) open reading frames (ORFs) . One strand ORF is 1,929 nucleotides long and exhibits great identity (87.5% at the nucleotide level and 94% at the amino acid level) with the hsp70 gene copies of D. melanogaster, while the second strand ORF, in antiparallel in-frame register arrangement, is 1,839 nucleotides l ong and exhibits 32% identity with a putative, recently identified, NA D(+)-dependent, glutamate dehydrogenase (NAD(+)-GDH). The overlap of t he two ORFs is 1,824 nucleotides long. Computational analysis shows th at this LAC ORF arrangement is conserved in other hsp70 loci in a wide range of organisms, raising questions about possible evolutionary ben efits of such a peculiar genomic organization.