beta-1,4-galactosylation of N-glycans is a complex process

Most beta-1,4-galactosyltransferase (beta-1,4-GalT)-knockout mice die after birth. Although several defects were found transiently in these animals, t he primary cause of death is obscure. Not only beta-1,4-linked galactose re sidues on N-glycans, but also beta-1,4-GalT activities were found in some o f the tissues. Recently, five human genes which encode beta-1,4-GalTs have been cloned, and the possible presence of such novel beta-1,4-GalTs in mice is considered to bring about survival of the mutant animal beyond birth. I n order to understand the semi-lethal nature of this animal, it is inevitab le to clarify how individual novel beta-1,4-GalTs are involved in the biosy nthesis of glycoconjugates based on their acceptor-substrate specificities. (C) 1999 Elsevier Science B.V. All rights reserved.