MAK21P OF SACCHAROMYCES-CEREVISIAE, A HOMOLOG OF HUMAN CAATT-BINDING PROTEIN, IS ESSENTIAL FOR 60 S-RIBOSOMAL-SUBUNIT BIOGENESIS

Mak21-1 mutants are unable to propagate M-1 double-stranded RNA, a sat ellite of the L-A double-stranded RNA virus, encoding a secreted prote in toxin lethal to yeast strains that do not carry M-1. We cloned MAK2 1 using its map location and found that Mak21p is homologous to a huma n and mouse CAATT-binding protein and open reading frames in Schizosac charomyces pombe and Caenorhabditis elegans, Although the human protei n regulates Hsp70 production, Mak21p is essential for growth and neces sary for 60 S ribosomal subunit biogenesis. mak21-1 mutants have decre ased levels of L-A coat protein and L-A double-stranded RNA. Electropo ration with reporter mRNAs shows that mak21-1 cells cannot optimally e xpress mRNAs which, like L-A viral mRNA, lack 3'-poly(A) or 5'-cap str uctures but can normally express mRNA with both cap and poly(A), The v irus propagation phenotype of mak21-1 is suppressed by ski2 or ski6 mu tations, each of which derepresses translation of non-poly(A) mRNA.