Mutational synergy of SNP1-(1-223) and SNP1-(1-208) with CBC2-Y24A
The Y24A mutation in the m7G-binding pocket of Cbc2 suppresses the tgs1∆ cs growth defect (Qiu et al. 2012), as do C-terminal truncations 1-223 and 1-208 of the U1 snRNP subunit Snp1. To query potential connections between Cbc2 and Snp1, we tested by plasmid shuffle the effects of the SNP1-(1-223) and SNP1-(1-208) alleles in CBC2snp1∆ and CBC2-Y24A snp1∆ strain backgrounds. We also tested in parallel the N-terminal truncation allele SNP1-(22-300), which eliminates a conserved peptide segment of Snp1/U1-70K that makes atomic contacts to the SmD3 and Yhc1/U1-C subunits of the U1 snRNP (Kondo et al. 2015; Schwer and Shuman 2015). Whereas SNP1-(22-300) caused no apparent growth defect in the CBC2-Y24A background, both SNP1-(1-223) and SNP1-(1-208) elicited a severe cold-sensitive defect in CBC2-Y24A cells (Figure 2), one that recapitulates the cold-sensitive growth defect of a cbc2∆ null strain (Qiu et al. 2012).
Figure 2  Mutational synergy of SNP1-(1-223) and SNP1-(1-208) with CBC2-Y24A. The wild-type and truncated SNP1 alleles were tested for activity by plasmid shuffle in CBC2 snp1∆ and CBC2-Y24A snp1∆ strains. FOA-resistant isolates were spot-tested for growth on YPD agar at the temperatures specified. Synthetic growth defects are denoted by •.