Using the murine cDNA that encodes Golgi alpha-mannosidase II (GlcNAc transferase I-dependent alpha 1,3[alpha 1,6] mannosidase; EC 22.214.171.124) as a probe to screen a cDNA library made from Drosophila melanogaster (Dm) embryos, we have isolated GmII, the Dm sequence homologue. The 3926-bp cDNA has an open reading frame of 3327 bp and predicts a polypeptide of approx. 127 kDa, a mass similar to that of the murine protein. The deduced mouse and Dm amino acid (aa) sequences share extensive similarity across their entire lengths and are both type-II transmembrane (TM) proteins with short cytoplasmic tails, single TM domains and large hydrophilic C-terminal domains. A region of approx. 200 aa, within the C-terminal domain, has considerable similarity to a corresponding region from several other alpha-mannosidases. GmII has been localized to a single site (85D14-18) on the right arm of chromosome 3.