Protein glycosylation at the asparagine residues (N-glycosylation) is essential for eukaryotic cell growth, and changes in this function have profound effects on cell physiology. To date, little is known about molecular controls in the N-glycosylation pathway and how the levels of N- glycosylation affect cell function. Recent studies by the principal investigator have shown that in the yeast Saccharomyces cerevisiae, which shares the early steps of N-glycosylation with higher eukaryotes, the activity of the N-glycosylation function is regulated at the very first step in the pathway catalyzed by the tunicamycin sensitive enzyme, N- acetylglucosamine-1-phosphate (ALG7) transferase. Interestingly, the cellular activity of this enzyme in yeast appears to be regulated ta the level of transcription. Such control of N-glycosylation is physiologically significant since changes in the cellular activity of the ALG7 transferase have dramatic effects on the yeast cell growth, development, and other functions. This also appears to be the case in higher, eukaryotes since alterations in the activity of this enzyme correlate with different developmental stages of sea urchin embryos. We now propose to examine transcription of the ALG7 transferase gene in a developing mammalian tissue. The postnatally developing hamster salivary submandibular gland provides an excellent model for studies of developmental control of N- linked glycoprotein biosynthesis. We will investigate changes in the ALG7 mRNA levels and the ALG7 transferase activity at different stages of hamster postnatal submandibular gland development. The ALG7-mRNAs will be detected with hamster-specific ALG7 probes consisting of synthetic olignucleotides and ALG7 cDNA clones. Our work will provide the first study of molecular controls of N-glycosylation in higher eukaryotes and assess the involvement of this function in development.
