The proteolipid subunit of the Neurospora crassa vacuolar ATPase: isolation of the protein and the vma-3 gene.

We have isolated the proteolipid subunit from the vacuolar ATPase of Neurospora crassa, using ion-exchange chromatography. We have also isolated several cDNA clones and the corresponding genomic DNA that encodes this subunit. The derived protein sequence indicates that the polypeptide is composed of 161 amino acid residues with an M(r) of 16,328 kDa. The gene encoding the proteolipid, named vma-3, is unusual in several respects. It contains four introns and, unlike other fungal genes, has non-coding regions that are as large as the coding regions. The 3' untranslated regions of the cDNAs were quite heterogeneous, with polyadenylation sites more than 300 bp apart. Analysis of the mRNA indicates that two size classes of transcripts are produced, differing in the length of the 3' untranslated region. Mapping of the vma-3 gene showed that it is closely linked, but not adjacent to, vma-1, the gene encoding the 67 kDa subunit of the vacuolar ATPase. This raises the possibility that in N. crassa some of the vacuolar ATPase genes may be clustered.