The KTR and MNN1 mannosyltransferase families of Saccharomyces cerevisiae

Glycosylation constitutes one of the most important of all the post-transla tional modifications and may have numerous effects on the function, structu re, physical properties and targeting of particular proteins. Eukaryotic gl ycan structures are progressively elaborated in the secretory pathway. Foll owing the addition of a core N-linked carbohydrate in the endoplasmic retic ulum, glycoproteins move to the Golgi complex where the elongation of O-lin ked sugar chains and processing of complex N-linked oligosaccharide structu res take place. In order to better define how such post-translational modif ications occur, we have been studying the yeast KTR and MNN1 mannosyltransf erase gene families. The KTR family contains nine members: KRE2, YUR1, KTR1 , KTR2, KTR3, KTR4, KTR5, KTR6 and KTR7. The MNN1 family contains six membe rs: MNN1, TTP1, YGL257c, YNR059w, YIL014w and YJL86w. In this review, we ad dress protein structure, sequence similarities and enzymatic activity in th e context of each gene family. In addition, a description of the known func tion of many family members in O- and N-linked glycosylation is included. F inally, the genetic interactions and functional redundancies within a gene family are also discussed. (C) 1999 Elsevier Science B.V. All rights reserv ed.