MOLECULAR AND GENETIC-ANALYSIS OF THE DROSOPHILA MAS-1 (MANNOSIDASE-1) GENE WHICH ENCODES A GLYCOPROTEIN PROCESSING ALPHA-1,2-MANNOSIDASE

Glycosylation is an important mechanism for modulating the physicochem ical and biological properties of proteins in a stage- and tissue-spec ific manner. The enzymology of this process is just beginning to be un derstood. Here we present the molecular analysis of mas-1 (mannosidase -1), a Drosophila gene with significant homologies to mammalian and Sa ccharomyces cerevisiae glycoprotein processing alpha 1,2-mannosidases. An enhancer-trap P-element inserted upstream of nas-1 leads to highly specific lacZ expression in the lobula plate giant neurons, cells tha t mediate the large-field optomotor response. This staining, however, seems to reflect only a small part of the complex expression pattern o f the mas-1 gene: Two promoters produce alternative transcripts that s how individual spatial distributions during embryonic development, inc luding a maternal contribution. Both transcripts code for type II tran smembrane proteins which differ in their N-terminal parts. Null mutant s in mas-1 display defects in the embryonic PNS, in the wing, and in t he adult eye. These findings illustrate that the processing of N-linke d glycans plays a functional role in Drosophila development, There is, however, ample evidence for genetic and biochemical redundancy in the mannose-trimming steps of this pathway. (C) 1995 Academic Press, Inc.