Figure 1.

RAM1 plasmid restored a-factor processing and export to the M1 and M10 mutants, as determined by a-factor halo assay. A CEN LEU2 RAM1 plasmid (YCpL-RAM1) or the CEN LEU2 vector (YCplac111) were transformed into the M1 and M10 mutant strains (JRY5388 and JRY5389) and the RAM1 parental strain (JRY5312 transformed with URA3 CEN MFA1-CAMQ plasmid, pJR1556). These MATa strains, which expressed a-factor–CAMQ as the only source of mating pheromone, were assayed for a-factor production by halo assay (see Materials and Methods). The indicated MATa strains were spotted onto a lawn of MATα sst2 cells and grown for 3 days; biologically active a-factor exported from the MATa strains arrested growth of the MATα sst2 cells, forming a zone of growth inhibition (halo) that is proportional to the amount of a-factor produced.