EVIDENCE THAT THE 16-KDA PROTEOLIPID (SUBUNIT-C) OF THE VACUOLAR H-ATPASE AND DUCTIN FROM GAP-JUNCTIONS ARE THE SAME POLYPEPTIDE IN DROSOPHILA AND MANDUCA - MOLECULAR-CLONING OF THE VHA16K GENE FROM DROSOPHILA()

The 16 kDa proteolipid (subunit c) of the eukaryotic vacuolar H+-ATPas e (V-ATPase) is closely related to the ductin polypeptide that forms t he connexon channel of gap junctions in the crustacean Nephrops norveg icus. Here we show that the major protein component of Manduca sexta g ap junction preparations is a 16 kDa polypeptide whose N-terminal sequ ence is homologous to ductin and is identical to the deduced sequence of a previously cloned cDNA from Manduca (Dow et al., Gene, 122, 355-3 60, 1999). We also show that a Drosophila melanogaster cDNA, highly ho mologous to the Manduca cDNA, can rescue Saccharomyces cerevisiae, def ective in V-ATPase function, in which the corresponding yeast gene, VM A3, has been inactivated. Evidence is presented for a single genetic l ocus (Vha16) in Drosophila, which in adults at least contains a single transcriptional unit. Taken together, the data suggest that in Drosop hila and Manduca, the same polypeptide is both the proteolipid subunit c component of the V-ATPase and the ductin component of gap junctions . The intron/exon structure of the Drosophila Vha16 is identical to th at of a human Vha16 gene, and is consistent with an ancient duplicatio n of an 8 kDa domain. A pilot study for gene inactivation shows that t ransposable P-elements can be easily inserted into the Drosophila duct in Vha16 gene. Although without phenotypic consequences, these can ser ve as a starting point for generation of null alleles.