The Heat-Shock Gene hsp83 of Drosophila auraria: Genomic Organization, Nucleotide Sequence, and Long Antiparallel Coupled ORFs (LAC ORFs)

Abstract

The genomic organization of the hsp83 gene of Drosophila auraria, a far-eastern endemic species belonging to the montium subgroup of the melanogaster species group, is presented here. Based on in situ hybridization on polytene chromosomes, cDNA and genomic clone mapping, nucleotide sequencing, and genomic Southern analysis, hsp83 is shown to be present as a single-copy gene at locus 64B on the 3L chromosome arm in D. auraria. This gene is organized into two exons separated by a 929-bp intron. The first exon represents the mRNA leader sequence and is not translated, while the coding region, having a length of 2,151 bp, is solely included in the second exon. Nucleotide sequence comparisons of D. auraria hsp83 with homologous sequences from other organisms show high conservation of the coding region (88-92% identity) in the genus Drosophila, in addition to the conserved genomic organization of two-exons-one-intron, of comparable size and arrangement. A phylogenetic tree based on the protein sequences of homologous genes from representative organisms is in accord with the accredited phylogenetic position of D. auraria. In the hsp83 gene region, a second case of long antiparallel coupled open reading frames (LAC ORFs) for this species was found. The antiparallel to the hsp83 gene ORF is 1,554 bases long, while the two ORFs overlap has a size of 1,548 bp. The anti-hsp83 ORF does not show significant homology to any known gene sequences. In addition, no similar LAC ORF structures were found in homologous gene regions of other organisms.