Asp56 in actin is critical for the full activity of the amino acid starvation‐responsive kinase Gcn2

Abstract

Eukaryotes harbour a conserved signalling pathway, called General Amino Acid Control (GAAC) in Saccharomyces cerevisiae, for overcoming amino acid starvation. Upon starvation, the protein kinase Gcn2, which phosphorylates the eukaryotic translation initiation factor eIF2α, becomes stimulated to trigger the GAAC response. Genetic studies suggest that Yih1, which is the yeast homolog of mammalian IMPACT and which binds monomeric actin, inhibits Gcn2 when released from actin. Here, we found that D56A substitution in actin (the act1‐9 allele) leads to reduced eIF2α phosphorylation, suggesting that the Asp56 residue is required for full Gcn2 activation. In the act1‐9 mutant, Yih1 overexpression further enhanced the sensitivity to amino acid starvation‐inducing drugs and further impaired eIF2α phosphorylation, suggesting that Gcn2 inhibition was mediated via Yih1. The D56A substitution may impair the actin–Yih1 interaction, directly or indirectly, thereby increasing the amount of Yih1 available to inhibit Gcn2.

Evidence that Xrn1 is in complex with Gcn1, and is required for full levels of eIF2α phosphorylation

“…The cue that triggers Yih1/IMPACT to inhibit Gcn2 remains to be uncovered. So far it is only known that actin dynamics affects IMPACT's ability to inhibit Gcn2 [ 25 , 29 ]. Gir2 in yeast, or DFRP2 in mammals, also contains an N-terminal RWD domain, and so far for Gir2 it has been shown that it inhibits Gcn2 by binding to Gcn1, as found for Yih1/IMPACT [ 30 ].…”