Key result
Mak21p, a homolog of human CAATT-binding protein, is essential for 60 S ribosomal subunit biogenesis and optimal expression of mRNAs lacking 3'-poly(A) or 5'-cap structures in yeast.
Mak21p is identified as an essential protein for 60 S ribosomal subunit biogenesis and translation of specific mRNAs in yeast.
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Yeast data require mammalian validation before clinical inference; leaves open human CAATT-binding protein roles in 60S biogenesis or noncanonical translation.
Mak21-1 mutants are unable to propagate M1 double-stranded RNA, a satellite of the L-A double-stranded RNA virus, encoding a secreted protein toxin lethal to yeast strains that do not carry M1. We cloned MAK21 using its map location and found that Mak21p is homologous to a human and mouse CAATT-binding protein and open reading frames in Schizosaccharomyces pombe and Caenorhabditis elegans. Although the human protein regulates Hsp70 production, Mak21p is essential for growth and necessary for 60 S ribosomal subunit biogenesis. mak21-1 mutants have decreased levels of L-A coat protein and L-A double-stranded RNA. Electroporation with reporter mRNAs shows that mak21-1 cells cannot optimally express mRNAs which, like L-A viral mRNA, lack 3'-poly(A) or 5'-cap structures but can normally express mRNA with both cap and poly(A). The virus propagation phenotype of mak21-1 is suppressed by ski2 or ski6 mutations, each of which derepresses translation of non-poly(A) mRNA.
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Edskes et al. (1998) studied this question. Mak21-1 mutation was evaluated on 60 S ribosomal subunit biogenesis and M1 double-stranded RNA propagation. Mak21p, a homolog of human CAATT-binding protein, is essential for 60 S ribosomal subunit biogenesis and optimal expression of mRNAs lacking 3'-poly(A) or 5'-cap structures in yeast.
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