The biochemical defects of prp 4-1 and prp & 1 yeast splicing mutants reveal that the PRP 6 protein is required for the accumulation of the [ U 4 / U 6 . U 5 ] tri-snRNP

We have raised specific antibodies against the PRP6 protein and shown that the U4, U5 and U6 snRNAs are co-preclpltated with this protein. Using splicing extracts prepared from In vivo heat-Inactivated cells, we have characterized the prp4-1 and prp6-1 biochemical defects. In Inactivated prp4-1 cell extracts, the U6 snRNA content as well as the U6, U4/U6 snRNPs and the [U4/U6.U5] trl-snRNP particles amounts are severely reduced. In Inactivated prp6-1 cell extracts, the PRP6 mutant protein Is barely detectable. Glycerol gradient analyses indicate that, In these extracts, the [U4/U6.U5] tri-snRNPs are present In very low amounts, but U4/U6 snRNP particles are normally represented. These results establish that the PRP6 protein Is required for the accumulation of the [U4/U6.U5] trisnRNP. We found no evidence for the presence of the PRP6 protein In the U4/U6 particle.