GCN20, a novel ATP binding cassette protein, and GCN1 reside in a complex that mediates activation of the eIF-2 alpha kinase GCN2 in amino acid-starved cells.

Abstract

GCN2 is a protein kinase that phosphorylates the alpha‐subunit of translation initiation factor 2 (eIF‐2) and thereby stimulates translation of GCN4 mRNA in amino acid‐starved cells. We isolated a null mutation in a previously unidentified gene, GCN20, that suppresses the growth‐inhibitory effect of eIF‐2 alpha hyperphosphorylation catalyzed by mutationally activated forms of GCN2. The deletion of GCN20 in otherwise wild‐type strains impairs derepression of GCN4 translation and reduces the level of eIF‐2 alpha phosphorylation in vivo, showing that GCN20 is a positive effector of GCN2 kinase function. In accordance with this conclusion, GCN20 was co‐immunoprecipitated from cell extracts with GCN1, another factor required to activate GCN2, and the two proteins interacted in the yeast two‐hybrid system. We conclude that GCN1 and GCN20 are components of a protein complex that couples the kinase activity of GCN2 to the availability of amino acids. GCN20 is a member of the ATP binding cassette (ABC) family of proteins and is closely related to ABC proteins identified in Caenorhabditis elegans, rice and humans, suggesting that the function of GCN20 may be conserved among diverse eukaryotic organisms.

YIH1 Is an Actin-binding Protein That Inhibits Protein Kinase GCN2 and Impairs General Amino Acid Control When Overexpressed

“…The uncharged tRNA binds to a regulatory domain in GCN2 that resembles histidyl-tRNA synthetase, and this interaction is believed to induce a conformational change that overcomes an intrinsic defect in the adjacent kinase domain (7)(8)(9)(10). The products of GCN1 and GCN20 are also necessary for the activation of GCN2 by uncharged tRNA in starved cells (11,12). GCN1 and GCN20 form a protein complex (12) that binds to the N-terminal domain (NTD) of GCN2, which is highly conserved among all GCN2 orthologs.…”

“…The products of GCN1 and GCN20 are also necessary for the activation of GCN2 by uncharged tRNA in starved cells (11,12). GCN1 and GCN20 form a protein complex (12) that binds to the N-terminal domain (NTD) of GCN2, which is highly conserved among all GCN2 orthologs. The GCN2 NTD is required for kinase function in vivo, and its overexpression impairs complex formation between native GCN1 and GCN2 and produces a dominant Gcn Ϫ (general control noninducible) phenotype (13,14).…”

Can ABCF2 protein expression predict the prognosis of uterine cancer?

“…Evaluation of ABCF2 positives were reported previously (Tsuda et al, 2005a;Nishimura et al, 2007). ATP-binding cassette superfamily F2 protein is a member of ABC transporter superfamily and the GCN20 subfamily (Vasquez de Aldana et al, 1995) and we demonstrated that ABCF2 protein is predominantly located in the cytoplasm of cells (Tsuda et al, 2005a;Nishimura et al, 2007). Thus, in this study, we judged the positivities of this protein based on the cytoplasmic staining into either positive or negative.…”

“…In ovarian CCC, ABCF2 expression was associated with chemoresistance and OS (Tsuda et al, 2005a, b;Ogawa et al, 2006), while in breast cancer, lack of ABCF2 expression was associated with increased diseasefree survival (Ogawa et al, 2006). ATP-binding cassette superfamily F2 is a member of the GCN20 subfamily of the ABC transporter superfamily (Vasquez de Aldana et al, 1995). Similar to other members of the ABC family, ABCF2 contains a pair of nucleotidebinding domains but it lacks a transmembrane domain (Allikmets et al, 1996;Kerr, 2004), suggesting that it is unlikely to function as a cell membrane transporter, as do other members of the ABC family.…”

“…ATP-binding cassette superfamily F2 is a member of the GCN20 subfamily of the ABC transporter superfamily (Vasquez de Aldana et al, 1995;Allikmets et al, 1996;Kerr, 2004). Yasui et al reported that the ABCF2 gene is amplified in a chemoresistant ovarian cancer cell line (t24/cDDp10), with chromosome gain at 7q34 -36 (Yasui et al, 2005).…”