Saccharomyces cerevisiae ER membrane protein complex subunit 4 (EMC4) plays a crucial role in eIF2B-mediated translation regulation and survival under stress conditions.

BACKGROUND:Eukaryotic initiation factor 2B (eIF2B) initiates and regulates translation initiation in eukaryotes. eIF2B gene mutations cause leukoencephalopathy called vanishing white matter disease (VWM) in humans and slow growth (Slg^-) and general control derepression (Gcd^-) phenotypes in Saccharomyces cerevisiae. RESULTS:To suppress eIF2B mutations, S. cerevisiae genomic DNA library was constructed in high-copy vector (YEp24) and transformed into eIF2B mutant S. cerevisiae strains. The library was screened for wild-type genes rescuing S. cerevisiae (Slg^-) and (Gcd^-) phenotypes. A genomic clone, Suppressor-I (Sup-I), rescued S. cerevisiae Slg^- and Gcd^- phenotypes (gcd7-201 gcn2∆). The YEp24/Sup-I construct contained truncated TAN1, full length EMC4, full length YGL230C, and truncated SAP4 genes. Full length EMC4 (chaperone protein) gene was sub-cloned into pEG (KG) yeast expression vector and overexpressed in gcd7-201 gcn2∆ strain which suppressed the Slg^- and Gcd^- phenotype. A GST-Emc4 fusion protein of 47 kDa was detected by western blotting using α-GST antibodies. Suppression was specific to gcd7-201 gcn2∆ mutation in eIF2Bβ and Gcd1-502 gcn2∆ in eIF2Bγ subunit. Emc4p overexpression also protected the wild type and mutant (gcd7-201 gcn2∆, GCD7 gcn2∆, and GCD7 GCN2∆) strains from H₂O₂, ethanol, and caffeine stress. CONCLUSIONS:Our results suggest that Emc4p is involved in eIF2B-mediated translational regulation under stress and could provide an amenable tool to understand the eIF2B-mediated defects.

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