Figure 8.

mms21-SA cannot suppress smc5 and is synthetically lethal with it. (a) Suppression of smc5 temperature sensitivity by Mms21p requires the SUMO ligase activity of Mms21p. SMC5 (yGC141), smc5-31 (yGC231), and smc5-33 (yGC233) cells were transformed with either pRS316 or a 2μ vector with the indicated gene driven by the GAL1 promoter. Twenty-five thousand, 5000, 1000, 200, and 40 cells were plated. The overall level of suppression was lower than that in Figure 7a, as cells were grown for 2.5 days. (b) Mms21p promotes survival of smc5 cells at the restrictive temperature. This was done as in Figure 7c. (c) The smc5 and mms21-SA alleles are synthetically lethal. MMS21 or mms21-SA cells containing SMC5 on a URA3 plasmid and SMC5, smc5-31, or smc5-33 on a LEU2 plasmid (yGC301–306) were grown on 5-FOA medium at 22° for 5 days. This assay was done in triplicate with independent transformants. On one FOA plate there was slight growth of some smc5-33 mms21-SA cells. (d) Hypomorphism of smc5 alleles rescues the nibbled-colony morphology of “wild-type” yGC141. yGC141 (SMC5), yGC231 (smc5-31), and yGC233 (smc5-33) cells were grown for 5 days on YPAD at 22°.