Evidence that GCD6 and GCD7, Translational Regulators of GCN4, Are Subunits of the Guanine Nucleotide Exchange Factor for eIF-2 in Saccharomyces cerevisiae

Abstract

Starvation of the yeast Saccharomyces cerevisiae for an amino acid signals increased translation of GCN4, a transcriptional activator of amino acid biosynthetic genes. We have isolated and characterized the GCD6 and GCD7 genes and shown that their products are required to repress GCN4 translation under nonstarvation conditions. We find that both GCD6 and GCD7 show sequence similarities to components of a high-molecular-weight complex (the GCD complex) that appears to be the yeast equivalent of translation initiation factor 2B (eIF-2B), which catalyzes GDP-GTP exchange on eIF-2. Furthermore, we show that GCD6 is 30% identical to the largest subunit of eIF-2B isolated from rabbit reticulocytes. Deletion of either GCD6 or GCD7 is lethal, and nonlethal mutations in these genes increase GCN4 translation in the same fashion described for defects in known subunits of eIF-2 or the GCD complex; derepression of GCN4 is dependent on short open reading frames in the GCN4 mRNA leader and occurs independently of eIF-2 alpha phosphorylation by protein kinase GCN2, which is normally required to stimulate GCN4 translation. Together, our results provide evidence that GCD6 and GCD7 are subunits of eIF-2B in S. cerevisiae and further implicate this GDP-GTP exchange factor in gene-specific translational control.

Yeast Uri1p promotes translation initiation and may provide a link to cotranslational quality control

“…Gcd10p is required for tRNAi Met modification, and therefore gcd10‐503 cells exhibit reduced levels of TC, leading to derepression of GCN4 (Anderson et al , 1998). Likewise, Gcd6p, a subunit of the initiation factor eIF2B, which acts as a GEF for eIF2 (Bushman et al , 1993), is required for high TC levels. Wild‐type cells treated with 10 μg/ml diazaborine induce articulate halfmers, which indeed were reduced in gcd10‐503 and to a smaller extent in gcd6‐1 cells (Figure 3C; Supplementary Figure 2).…”

GTP binding to translation factor eIF2B stimulates its guanine nucleotide exchange activity

“…The following references appear in the Supplemental information : Bushman et al., 1993 ; Hill and Struhl, 1988 ; Jones, 1991 ; Mohammad-Qureshi et al., 2007a ; Richardson et al., 2004 ; Sievers et al., 2011 ; Sikorski and Hieter, 1989 ; Wek et al., 1990 ; Yang and Hinnebusch, 1996 .…”