The Calcofluor white-hypersensitive mutants cwh52 and cwh53 are severely reduced in beta 1,3-glucan. CWH52 was equivalent to GAS1. CWH53 represented a new gene, located on the right arm of chromosome XII, and predicted to encode a 215 kDa protein with multiple transmembrane domains. The transcription of CWH53 was cell cycle-dependent and, similar to GAS1/CWH52, increased in late G1, indicating that the formation of beta-glucan is cell cycle-regulated. Further, in some mutant alleles of both gas1/cwh52 and cwh53 lethal concentrations of Calcofluor induced growth arrest at a specific phase of the cell cycle.