To gain insights to the basis for tgs1∆ cold sensitivity, we sought to identify genetic suppressors that restore the growth of tgs1∆ cells at restrictive temperature . Based on our findings that the residual m7G cap of the U1 snRNP in tgs1∆ cells is accessible to and occupied by nuclear CBC, we queried whether mutating the cap-binding site of CBC (in the Cbc2 subunit of yeast CBC) might suppress tgs1∆ cs growth. We thereby identified a series of hypomorphic mutations of Cbc2 predicted to weaken cap-binding (Mazza et al. 2002; Calero et al. 2002), which had no effect on vegetative growth in TGS1 cells yet restored the growth of tgs1∆ cells at 18°–20° (Schwer et al. 2011; Qiu et al. 2012) . We inferred from these results that the cs phenotype is caused, at least in part, by the ectopic association of nuclear CBP with the m7G cap of U1 snRNA.