[Comparative research on two different killer strains of Saccharomyces cerevisiae]

Using two different killer strains SK4(K1 type) and ERR1(K2 type), their killer characters were analysed and find two strains compete with each other when they are mixed and killer characters are related with the growth of strains. Different M-dsRNA plasmids in different killer strains have different molecular lengths, being 1.7 kb and 1.5 kb in SK4 and ERR1, respectively. L-dsRNA plasmids in both strains have the same molecular lengths, 4.0 kb. Cured by high temperature (38 degrees C) and U.V. (15 W, 30 cm, 5 min), killer strains lose their killer characters with the disappearance of M-dsRNA, the curing rate of killer activity is associated with strains and curing conditions. Killer toxins produced by two strains have different killer effects. Toxins of SK4 and ERR1 have the different highest killer activity at pH 4.8, 16 degrees C and pH4.2, 22 degrees C, but both of two toxins have the greatest effect on the sensitive strain in the late-log phase.