POTENTIAL RNA-BINDING PROTEINS IN SACCHAROMYCES-CEREVISIAE IDENTIFIEDAS SUPPRESSORS OF TEMPERATURE-SENSITIVE MUTATIONS IN NPL3

The NPL3 gene of the yeast Saccharomyces cerevisiae encodes a protein with similarity to heterogeneous nuclear ribonucleoproteins (hnRNPs). Npl3p has been implicated in many nuclear-related events including RNA export, protein import, and rRNA processing. Several temperature-sens itive alleles of NPL3 have been isolated. We now report the sequence o f these alleles. For one allele, npl3-1, four complementation groups o f suppressors have been isolated. The cognate genes for the two recess ive mutants were cloned. One of these is the previously known RNA15, w hich, like NPL3, also encodes a protein with similarity to the vertebr ate hnRNP A/B protein family. The other suppressor corresponds to a ne wly defined gene we term HRP1, which also encodes a protein with simil arity to the hnRNP A/B proteins of vertebrates. Mutations in HRP1 supp ress all npl3 temperature-sensitive alleles but do not bypass an npl3 null allele. We show that HRP1 is essential for cell growth and that t he corresponding protein is located in the nucleus. The discovery of t wo hnRNP homologues that can partially suppress the function of Npl3p, also an RNA binding protein, will be discussed in terms of the possib le roles for Npl3p in RNA metabolism.