This study reports the cloning, sequencing, and
development of antisera against the human U5 snRNP 220-kDa
protein or hPrp8p. Prp8p is the most highly conserved large
nuclear protein known to date, but it is not related to
any other protein. Southern, Northern, and expressed sequence
tag analyses indicate that hPrp8p is encoded by a single
gene. Prp8p is a core component of U5 snRNP and the U4/U6.U5
tri-snRNP, and antibodies raised against it immunoprecipitate
both the major, U2-dependent and minor, U12-dependent spliceosomes.
These spliceosomes, which excise different classes of introns,
contain distinct sets of snRNAs overlapping only with U5
snRNA. Other than the core Sm proteins, hPrp8p is the first
splicing factor shown to be common to both spliceosomes.