One of the most attractive areas of Biology is the knowledge of how organisms generate and maintain their shape. In fungi, the cell wall is an essential morphogenetic element, since it is the last organelle responsible for the maintenance of the cellular shape. Our objective is to study how the biosynthesis of β-glucan, an essential component of the cell wall, is regulated by the mechanisms of vesicular transport. In this work we have addressed the study of the regulation of the synthesis of this polymer by the Cfr1/Csr1p complex. Cfr1p and Csr1p share similarity with the exomer proteins from S. cerevisiae. The term exomer refers to a set of proteins that form a vesicle coat required for the transport of certain proteins from the trans-Golgi network to the plasma membrane. The exomer is formed by a scaffold protein, Chs5p, to which Chs6p and its homologues (Bch1p, Bud7p and Bch2p, termed generically “ChAPs”) anchor. The ChAPs are responsible for cargo specificity. S. pombe Cfr1p shares similarity with Chs5p and Csr1p is the only protein similar to the ChAPs. Previous studies have shown that Cfr1p localizes at the Golgi and is required for cell fusion during mating, a function that shares with Chs5p. We have cloned csr1+ and have found that Cfr1p and Csr1p form a complex at the Golgi and that the localization of each protein in this organelle depends on each other. Additionally, cfr1Δ and csr1Δ mutants are sensitive to compounds that interfere with cell wall synthesis, interact genetically with mutants in the β(1,3)glucan synthase, and have a reduced level of β-glucan in their cell wall. Our goal is to study the role that these proteins might play in vesicular transport, and to determine how they regulate cell wall synthesis and morphogenesis.

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