Polymerizes chitin, a structural polymer of the cell wall and septum, by transferring the sugar moiety of UDP-GlcNAc to the non-reducing end of the growing chitin polymer (PubMed:2140148). Also involved in forming cross walls in the hyphal phase (PubMed:2140148). [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + UDP-N-acetyl-alpha-D-glucosamine = [(1->4)-N-acetyl-beta-D-glucosaminyl](n+1) + H(+) + UDP Requires proteolytic activation. Yeast and hyphal stages, the latter having a higher specific activity. Under certain adverse conditions. Belongs to the chitin synthase family. It is uncertain whether Met-1 or Met-58 is the initiator.