Using GCN4 as a reporter of eIF2 alpha phosphorylation and translational regulation in yeast

Molecular genetic analyses in yeast are a powerful method to study gene regulation. Conservation of the mechanism and regulation of protein synthesis between yeast and mammalian cells makes yeast a good model system for the analysis of translation. One of the most common mechanisms of translational regulation in mammalian cells is the phosphorylation of serine-51 on the ct subunit of the translation initiation factor eIF2, which causes an inhibition of general translation. In contrast, in the yeast Saccharomyces cerevisiae phosphorylation of eIF2 alpha on serine-51 by the GCN2 protein kinase mediates the translational induction of GCN4 expression. The unique structure of the GCN4 mRNA makes GCN4 expression especially sensitive to eIF2 alpha phosphorylation, and the simple microbiological tests developed in yeast to analyze GCN4 expression serve as good reporters of eIF2 alpha phosphorylation. it is relatively simple to express heterologous proteins in yeast, and it has been shown that the mammalian eIF2 alpha kinases will functionally substitute for GCN2. Structure-function analyses of translation factors or translational regulators can also be performed by assaying for effects on general and GCN4-specific translation. Three tests can be used to study eIF2 alpha phosphorylation and/or translational activity in yeast. First, general translation can be monitored by simple growth tests, while GCN4 expression can be analyzed using sensitive replica-plating tests. Second, GCN4 translation can be quantitated by measuring expression from GCN4-IacZ reporter constructs. Finally, isoelectric focusing gels can be used to directly monitor in vivo phosphorylation of eIF2 alpha in yeast. (C) Academic Press.