THE YEAST EGD2 GENE ENCODES A HOMOLOG OF THE ALPHA-NAC SUBUNIT OF THE HUMAN NASCENT-POLYPEPTIDE-ASSOCIATED COMPLEX

Two Saccharomyces cerevisiae proteins of 21 and 27 kDa co-purify with a novel enhancer of Ga14p DNA binding activity (Egdp) [Parthun et al., Mel. Cell. Biol. 12 (1992) 5683-5689]. Mutations in the EGD1 gene encoding the 21-kDa protein (Egd1p) have been shown to affect the kinetics and extent of the Gal4p-mediated, galactose-induced activation of the GAL genes. Egd1p is homologous to human BTF3b, recently identified as the beta subunit of the heterodimeric nascent-polypeptide-associated complex (NAG) involved in ensuring signal-sequence-specific protein sorting and translocation [Wiedmann et al., Nature 370 (1994) 434-440]. We have cloned and characterized EGD2 encoding the 27-kDa protein and found that Egd2p is strikingly similar to the alpha subunit of human NAG. Yeast, therefore, contains a complex composed of Egd1p and Egd2p very similar to the NAC complex described in human cells. Disruption of EGD2, alone or in combination with an EGD1 disruption, causes no obvious phenotypes. The lack of phenotype, the high levels of EGD1 and EGD2 expression, and the identification of multiple human genes encoding NAC subunits suggest that the yeast EGD genes may be members of multigene families with redundant function.