Alternate catalytic subunit of the 1,3-beta-glucan synthase (GS). Synthesizes 1,3-beta-glucan, a major structural component of the yeast cell wall. Required for spore wall assembly. Negative regulation of activity by SMK1 is important for spore wall deposition. Activity is positively regulated by RHO1. [(1->3)-beta-D-glucosyl](n) + UDP-alpha-D-glucose = [(1->3)-beta-D-glucosyl](n+1) + H(+) + UDP Component of the 1,3-beta-glucan synthase (GS), composed of two alternate catalytic subunits FKS1 or GSC2, and a regulatory subunit RHO1. Interacts with SMK1. Under starvation and during sporulation. Also by pheromones and calcium in a calcineurin-dependent manner. Deletion leads to caspofungin resistance. Belongs to the glycosyltransferase 48 family.