THE ISOLATION, LOCALIZATION AND CHARACTERIZATION OF THE QM HOMOLOG INDROSOPHILA-MELANOGASTER

A fragment of 443 bp was amplified from a lambda ZAPII Drosophila cent ral nervous system (CNS) cDNA library using minimally degenerate prime rs to very conserved regions of the QM gene. This fragment was used as a probe to screen the lambda ZAPII Drosophila CNS cDNA library. Two c lones of the Drosophila QM homolog (pDQM-7A1 and pDQM-2B1), each conta ining the complete coding region, were isolated. The 5'-UTR of this ge ne was obtained by RACE PCR and ligated to the coding sequence to prod uce a the full-length copy of the Drosophila QM homolog (DQM) cDNA. Th e DQM cDNA measures 746 nucleotides in length and encodes a polypeptid e of 218 residues. The amino acid sequence shows 76.1 percent identity with human QM and 69.1 percent identity with QSR1, the yeast homolog of QM. Unlike the human or mouse genome which contains multiple copies of the QM gene, the Drosophila genome has only a single copy as indic ated by genomic Southern blot analysis. In situ hybridization confirms the presence of a single copy of DQM in the Drosophila genome and loc alizes it to the left arm of the third chromosome at the end of region 80A (80A-4).