Fidelity of HIS4 start codon selection influences 3-amino-1,2,4-triazole sensitivity in GTPase activating protein function defective eIF5

Abstract

The eIF5 protein plays an important role in the fidelity of AUG start codon selection. However, the hyper GTPase eIF5\[^{\mathrm{G31R}}\] mutation in yeast causes preferential utilization of UUG as initiation codon and is termed as suppressor of initiation codon (Sui\[^{-}\]) phenotype. The eIF5\[^{\mathrm{G31R}}\] mutant recognizes upUUG initiation codon from the 5\[^{\prime }\] regulatory leader region of GCN4 transcript and dominantly represses GCN4 expression thereby conferring sensitivity to 3-amino-1,2,4-triazole (3AT)-induced starvation. The 3AT sensitivity was rescued by supplementing HIS4\[^{UUG}\] allele. The eIF5\[^{\mathrm{G31R}}\] mutant has a better efficiency of UUG codon recognition from the HIS4\[^{UUG}\] allele under starvation conditions. Moreover, the expression of HIS4\[^{UUG}\] allele was significantly lower than the critical level causing additional derepression of GCN4 expression in eIF5\[^{\mathrm{G31R}}\] mutant to rescue its 3AT sensitivity. The overexpression of eIF1 improved expression of HIS4\[^{AUG}\] allele and GCN4 transcript causing 3AT resistance, whereas overexpression of eIF1 resulted in diminished UUG codon recognition of HIS4\[^{UUG}\] allele causing 3AT sensitivity, despite having higher GCN4 expression. This paper reports the critical role of HIS4 expression necessary in response to 3AT-induced starvation in the eIF5\[^{\mathrm{G31R}}\] mutant which is ostensibly not a direct target of 3AT inhibition.