THE BIOCHEMICAL DEFECTS OF PRP4-1 AND PRP6-1 YEAST SPLICING MUTANTS REVEAL THAT THE PRP6 PROTEIN IS REQUIRED FOR THE ACCUMULATION OF THE [U4 U6.U5] TRI-SNRNP/

We have raised specific antibodies against the PRP6 protein and shown that the U4, U5 and U6 snRNAs are co-precipitated with this protein. U sing splicing extracts prepared from in vivo heat-inactivated cells, w e have characterized the prp4-1 and prp6-1 biochemical defects. In ina ctivated prp4-1 cell extracts, the U6 snRNA content as well as the U6, U4/U6 snRNPs and the [U4/U6.U5] tri-snRNP particles amounts are sever ely reduced. In inactivated prp6-1 cell extracts, the PRP6 mutant prot ein is barely detectable. Glycerol gradient analyses indicate that, in these extracts, the [U4/U6.U5] tri-snRNPs are present in very low amo unts, but U4/U6 snRNP particles are normally represented. These result s establish that the PRP6 protein is required for the accumulation of the [U4/U6.U5] tri-snRNP. We found no evidence for the presence of the PRP6 protein in the U4/U6 particle.