The multigene family of the tobacco hornworm V-ATPase: novel subunits a, C, D, H, and putative isoforms.

The plasma membrane V-ATPase from Manduca sexta (Lepidoptera, Sphingidae) larval midgut is composed of at least 12 subunits, eight of which have already been identified molecularly [Wieczorek et al., J. Bioenerg. Biomembr. 31 (1999) 67-74]. Here we report primary sequences of subunits C, D, H and a, which previously had not been identified in insects. Expression of recombinant proteins, immunostaining and protein sequencing demonstrated that the corresponding proteins are subunits of the Manduca V-ATPase. Genomic Southern blot analysis indicated the existence of multiple genes encoding subunits G, a, c, d and e. Moreover, multiple transcripts were detected in Northern blots from midgut poly(A) RNA for subunits B, G, c and d. Thus, these polypeptides appear to exist as multiple isoforms that could be expressed either in different tissues or at distinct locations within a cell. By contrast subunits A, C, D, E, F and H appear to be encoded by single transcripts and therefore should be present in any Manduca V-ATPase, independent of its subcellular or cell specific origin.