Pre-mRNA Processing Factor 18 (PRPF18)

PRP18 binds transiently to the spliceosome just before the second transesterification reaction and after other stages within the second step. Functional analyses indicated that yeast Prp18 can substitute for human PRP18 in the splicing reaction but not vice versa.The deduced 342-amino acid human PRP18 protein is 91 amino acids longer than the yeast Prp18 protein, but they share 31% amino acid identity. Homology is strongest in the C-terminal third of the proteins. Western blot analysis showed that PRP18 is expressed as a 40-kD protein, and anti-PRP18 cross-reacted with a 55-kD protein. The 55-kD protein did not appear to be either a modified form or an alternatively spliced form of PRP18 and was shown to be associated with RNU4 and RNU6.