As previously reported, in a wild-type background, the U2-IIc allele confers a slow growth phenotype consistent with its defect in splicing. However, the U2-IIa allele confers no growth defect or splicing defect. Expression of the mutant U2-IIa or U2-IIc snRNA allele does not alter the growth of bur2D. Similarly, the slowgrowth phenotype conferred by CTK2 deletion is not altered by the U2 structural mutants. These data suggest that, like CUS2, neither the U2-IIc nor the U2-IIa conformation displays functional overlap with the Bur or Ctk complexes. Because of the orthologous relationship between the Bur complex and the P-TEFb complex, we looked closely at a variety of readouts associated with Bur complex function. Deletion of BUR2 results in several phenotypes that are classic indicators of defects in transcription, including sensitivity to the drug 6-azauracil. Treatment of cells with 6-AU results in nucleotide depletion and enhances the requirement for a fully functioning transcription apparatus for efficient transcription. Hence, genes encoding transcription elongation factors are often required for cell viability in the presence of 6-azauracil. If CUS2 is involved in regulating transcription elongation through Y-27632 dihydrochloride interactions with the Bur complex, then it is likely that CUS2 will also exhibit this phenotype or affect the 6-AU sensitivity of bur2 mutants. Deletion of BUR2 results in several phenotypes that are classic indicators of defects in transcription, including sensitivity to the drug 6-azauracil. Treatment of cells with 6-AU results in nucleotide depletion and enhances the requirement for a fully functioning transcription apparatus for efficient transcription. Hence, genes encoding transcription elongation factors are often required for cell viability in the presence of 6-azauracil. If CUS2 is involved in regulating transcription elongation through interactions with the Bur complex, then it is likely that CUS2 will also exhibit this phenotype or affect the 6-AU sensitivity of bur2 mutants. grown on media lacking inositol. It is possible that the U2 snRNP may affect transcription but that in vivo this activity may only be revealed under certain conditions. The role for the Bur and Ctk complexes has been characterized, in part, by their genetic interactions with other components of the transcription apparatus. To address whether a U2 snRNP function in transcription can be revealed through functional interactions with elongation factors, we performed a targeted genetic screen between CUS2 or the U2 snRNA and factors known to interact with the CDKs. Previous studies have suggested that transcription and splicing are functionally coupled. A key prediction of this model is that specific transcription factors and splicing factors physically interact and that these interactions would affect splicing, transcription, or both. Mammalian studies have demonstrated such a relationship between the transcriptional elongation factors P-TEFb and Tat- SF1. The experiments described here set out to determine whether the yeast homologs of P-TEFb and components of the U2 snRNP have similar physical and functional interactions. We find that the U2 snRNP components do not affect transcription in a detectable way. Furthermore, we were unable to detect physical interactions between the U2 snRNP components and the P-TEFb homologs. Taken together, we find a lack of evidence for a functional interaction between the P-TEFb homologs and the yeast U2 snRNP, particularly in transcription. Our findings do not eliminate the possibility that the U2 snRNP plays some role in transcription, perhaps of specific genes under specific PLX-4720 conditions not tested in this study. However, if such a role exists, it does not appear to generally involve interactions with the Bur or Ctk complexes or their characterized roles in transcription. Although there were already suggestions in the literature that transcription and, in particular, the CTD of RNAPII could affect splicing, the work by Fong & Zhou was the first to demonstrate that specific interactions between the splicing and transcription machineries led to a reciprocal relationship between transcription and splicing.