The functioning of the yeast Golgi apparatus requires an ER protein encoded by ANP1, a member of a new family of genes affecting the secretory pathway.

Abstract

Mnt1p is an alpha 1.2‐mannosyltransferase which resides in an early compartment of the Saccharomyces cerevisiae Golgi apparatus. We have shown that the signal‐anchor region is sufficient, and the transmembrane domain necessary, for its normal Golgi localization. This is similar to the transmembrane domain‐mediated retention of mammalian glycosyltransferases, and distinct from the tail‐mediated recycling retention of certain mammalian and yeast trans‐Golgi proteins. To examine the mechanism involved in transmembrane domain‐mediated retention, we have isolated six classes of mutants which fail to retain Mnt1p‐reporter fusions in the early Golgi. These mutants all show additional phenotypes which are consistent with alterations in Golgi function. We have called the mutant classes ‘gem’, for Golgi enzyme maintenance. GEM3 is identical to the previously cloned gene ANP1, and homologous to VAN1 and MNN9. Together, these define a new class of proteins involved in the organization and functioning of the secretory pathway. Interestingly, Anp1p is localized to the endoplasmic reticulum (ER), implying that some function of the ER is required to maintain a functional Golgi apparatus.

Molecular analysis of CaMnt1p, a mannosyl transferase important for adhesion and virulence of Candida albicans

“…1B). This indicates that, like ScMnt1p, CaMnt1p is a type II membrane protein residing in a medial Golgi compartment (17). Overexpression of CaMnt1p in Pichia pastoris resulted in high mannosyl transferase activities, indicating that CaMNT1 encodes a mannosyl transferase rather than a regulator of expression of mannosyl transferases (L. Thomson, Y. Aoki, S. Yamazaki, E.T.B., and N.A.R.G., unpublished results).…”

“…Attachment of the first mannose to the protein in the endoplasmic reticulum (ER) is mediated by Pmt proteins and has been shown to be an essential process in yeast (14). Addition of the second and third mannose residues can be attributed to Ktr3p and Mnt1p (15,16), which are likely to be ␣-1,2-mannosyl transferases residing in a medial Golgi compartment (16,17). Transfer of the terminal ␣-1,3-mannose residues is mediated by Mnn1p in a medial Golgi compartment (18,19).…”

A Yeast Golgi E-type ATPase with an Unusual Membrane Topology

“…4, A-C). The staining pattern is typical of the yeast Golgi apparatus (44); it is also seem for endopeptidase Kex1p, dipeptidyl aminotransferase A, Ca ϩ2 -ATPase Pmr1p, Mnn1p, Gda1p, and Kex2p (36,(45)(46)(47)(48)(49). Because the copy number of the 2-m plasmid can vary between 10 and 40 copies per cell within a population (50), the number of distinct fluorescent spots corresponding to Apy1p-HA also varies from cell to cell, ranging from a weak signal to a very strong signal.…”

Chitin synthase III: Synthetic lethal mutants and “stress related” chitin synthesis that bypasses the CSD3/CHS6 localization pathway

“…The ANP1 gene is homologous to VAN1 and MNN9. Together, the three constitute a family of genes required for proper Golgi function in S. cerevisiae (43). To determine whether or not the other members of this gene family have the same synthetic lethal interaction with chs3, heterozygous diploids were constructed with mnn9 and van1.…”