(A) The map of the C-Z gene fragment. Primers 1F, 2F, 1R and 2R were designed based on this fragment. If the homologous recombination happens, PCR product using the primer set, 1F and 1R, is a 1443-bp fragment between 5’cbs and zeocin (PCR1). PCR product using the primer set, 2F and 2R, is a 1111-bp fragment between 3’cbs and zeocin (PCR2). PCR product using the primer set, 1F and 2R, is a 2800-bp fragment including cbs and zeocin (PCR3). (B) Identification of the Cbs disruption with PCRs. The genomic DNA was respectively extracted from different strains. The crossover of 5’ was identified by PCR1, the 3’crossover was identified by PCR2, and the knock-out of Cbs by the homologous recombination was identified by PCR3.