The yeast Saccharomyces cerevisiae makes a variety of glycoproteins, called mannoproteins owing to the high content of mannose. These mannoproteins contain both O- and N-linked carbohydrate chains, and differences in the structure of the carbohydrate component have been found between different mannoproteins and between mannoproteins localized to different parts of the cell. The synthesis of mature N-linked chains involves initiation of outer chain addition to the core precursor, followed by elongation, termination, branching, and then maturation by mannosylphosphorylation and alpha 1-3- mannosylation. The objective of this research is to investigate the enzymology of the termination reaction which regulates whether the N-linked chains are of the small or large type. A specific assay will be developed for the terminase activity so that it can be measured in the presence of other mannosyltransferases in crude extracts. The terminase will be purified by standard procedures, and factors that modulate its activity will be studied. Saccharomyces cerevisiae, common baker's yeast, provides a useful model for studies on eucaryotic development and on the structural function relationships of the carbohydrate component of glycoproteins. This work will lead to a better understanding of the developmental role of these compounds. Yeasts are important in biotechnology and the results of these studies may form the basis for developing new useful types of yeasts.
