csmA, a gene encoding a class V chitin synthase with a myosin motor-like domain of Aspergillus nidulans, is translated as a single polypeptide and regulated in response to osmotic conditions.

The csmA gene of Aspergillus nidulans encodes a polypeptide that consists of an N-terminal myosin motor-like domain and a C-terminal chitin synthase domain. csmA null mutants showed marked abnormalities in polarized growth, hyphal wall integrity, and conidiophore development. Furthermore, the growth of the csmA null mutants was sensitive to low osmotic conditions. In an effort to investigate the intracellular behavior of the csmA product (CsmA) and the regulation of its production, we constructed strains that produced CsmA tagged with nine repeats of the hemagglutinin A (HA) epitope at its COOH terminus (CsmA-HA) instead of CsmA. Western blot analysis with anti-HA antibody showed that the entire coding region of csmA was translated as a single polypeptide with an approximate molecular mass of 210kDa. CsmA-HA was produced during vegetative growth; however, its yield was significantly reduced under high osmotic conditions, suggesting that the role of CsmA in growth and morphogenesis is particularly important under low osmotic conditions.