Translation initiation region dependency of translation initiation in Escherichia coli by IF1 and kasugamycin

Translation initiation factor 1 (IF1) is an essential protein in prokaryotes. The nature of IF1 interactions with the mRNA during translation initiation on the ribosome remains unclear, even though the factor has several known functions, one of them being RNA chaperone activity. In this study, we analyzed translational gene expression in vivo in two cold-sensitive chromosomal mutant variants of IF1 with amino acid substitutions, R40D and R69L, using two different reporter gene systems. The strains with the mutant IF1 gave higher reporter gene expression than the control strain. The extent of this effect was dependent on the composition of the translation initiation region. The Shine-Dalgarno (SD) sequence, AU-rich elements upstream of the SD sequence and the region between the SD sequence and the initiation codon are important for the magnitude of this effect. The data suggest that the wild-type form of IF1 has a translation initiation region-dependent inhibitory effect on translation initiation. Kasugamycin is an antibiotic that blocks translation initiation. Addition of kasugamycin to growing wild-type cells increases reporter gene expression in a very similar way to the altered IF1, suggesting that the infA mutations and kasugamycin affect some related step in translation initiation. Genetic knockout of three proteins (YggJ, BipA, and CspA) that are known to interact with RNA causes partial suppression of the IF1-dependent cold sensitivity.