SNP1-(1-223) and SNP1-(1-208) suppress tgs1Δ
The standout finding was that the SNP1-(1-223) and SNP1-(1-208) truncation alleles restored the growth of tgs1∆ cells at 25° and 20° (Figure 1B) and at 18° (not shown). Colony size of the SNP1-(1-223) tgs1∆ and SNP1-(1-208) tgs1∆ strains on YPD medium at cold temperatures was indistinguishable from the SNP1TGS1 wild-type strain (Figure 1B). Thus, deletion of the Snp1 segment from aa 224-300, downstream of the RRM domain, elicited a gain-of-function for the U1 snRNP that lacks a TMG cap. This positive genetic interaction was severed when the C-terminal truncation was extended into the RRM domain, i.e., the SNP1-(1-193) tgs1∆ reverted to cs growth (à la tgs1∆) and acquired a new ts phenotype (Figure 1B).