Sequence-context dependency shown by eIF5G31Rmutant for UUG start codon selection inSaccharomyces cerevisiae

Abstract

ABSTRACTIn higher eukaryotes, the efficiency of start codon selection depends upon its sequence context A/GxxAUGG, especially at the −3 and +4 position. However,S. cerevisiaeprefers AAA/UAUGU sequence context surrounding the AUG start codon. Furthermore, it was demonstrated that the first AUG codon on the mRNA serves as a signal for ribosomal recognition of the initiation site selection. In yeast, the G31R mutation in eIF5 shows Suppressor of initiation codon (Sui−) phenotype enabling 40S ribosome to initiate at UUG start codon. To understand whether the UUG codon recognition by the eIF5G31Rmutant is sensitive to the sequence context, we made differentHIS4-LacZreporter constructs with UUG as start codon and changed the sequence context at −3 and −2 positions. The HIS4UUG-LacZ transcripts that carry purine (A/G) at the −3-position showed better ß-Galactosidase activity than pyrimidine (U/C). Furthermore, on changing the −1 position for the AAA context, we discovered purines are more preferred at the −1 position for the UUG start codon selection.