TRANSLATIONAL CONTROL OF GCN4 - AN IN-VIVO BAROMETER OF INITIATION-FACTOR ACTIVITY

Phosphorylation of translation initiation factor-2 (elF-2) is an adapt ive mechanism for downregulating protein synthesis under conditions of starvation and stress. The yeast Saccharomyces has evolved a sophisti cated means of increasing translation of GCN4 mRNA when elF-2 is phosp horylated, allowing the induction of an important stress-response prot ein when expression of most other genes is decreasing. Because transla tion of GCN4 mRNA is so tightly coupled to elF-2 activity, genetic ana lysis of this system has provided unexpected insights into the regulat ion of elF-2 and its guanine nucleotide exchange factor, elF-2B.