Isolation, characterization, and expression of cDNAs encoding murine alpha-mannosidase II, a Golgi enzyme that controls conversion of high mannose to complex N-glycans

Another potential role for the tail/transmembrane domain/stem regions of these Golgi enzymes would be in the recognition and retention of the polypeptides in the Golgi stacks. Recognition signals for soluble and membrane bound polypeptides in the ER have been described . The tetrapeptide recognition signal, KDEL, on the COOH termini of soluble, lumenal ER proteins results in their recognition and retention in the ER (31) . Recently, a recognition signal for ER type I transmembrane proteins has also been described (16, 33, 36, 47) with the recognition sequence KKXX at the COOH termini of the polypeptide sequences being recognized on the cytoplasmic face of the ER (47) . Deletions in the first of three transmembrane domains of the avian coronavirus El glycoprotein disrupted the cis-Golgi localization of this polypeptide suggesting that a membraneassociated region contains at least a portion of the information of Golgi targeting of this viral glycoprotein (23) . The Golgi cisternae have an additional level of complexity, however, since many of the endogenous Golgi enzymes exhibit distinctive sub-Golgi compartmentation . The mechanistic requirements necessary to yield these subtle differences in Golgi localization may therefore be more complex than the simple linear sequences involved in ER protein retention.