Abstract
Isoleucyl-tRNA synthetase (IleRS) is an aminoacyl-tRNA synthetase whose essential function is to aminoacylate tRNAIle with isoleucine. Like some other aminoacyl-tRNA synthetases, IleRS can mischarge tRNAIle and correct this misacylation through a separate post-transfer editing function. To explore the biological significance of this editing function, we created a ileS(T233P) mutant of Bacillus subtilis that allows tRNAIle mischarging while retaining wild-type Ile-tRNAIle synthesis activity. As seen in other species defective for aminoacylation quality control, the growth rate of the ileS(T233P) strain was not significantly different from wild-type. When the ileS(T233P) strain was assessed for its ability to promote distinct phenotypes in response to starvation, the ileS(T233P) strain was observed to exhibit a significant defect in formation of environmentally resistant spores. The sporulation defect ranged from 3-fold to 30-fold and was due to a delay in activation of early sporulation genes. The loss of aminoacylation quality control in the ileS(T233P) strain resulted in the inability to compete with a wild-type strain under selective conditions that required sporulation. These data show that the quality control function of IleRS is required in B. subtilis for efficient sporulation and suggests that editing by aminoacyl-tRNA synthetases may be important for survival under starvation/nutrient limitation conditions.
Highlights
Isoleucine-tRNA synthetase (IleRS) possesses QC functions that discriminate between isoleucine, the non-cognate amino acid valine, and the non-proteinogenic amino acids, norvaline, a byproduct of branched-chain amino acid synthesis, and homocysteine (Hcy), a by-product from degradation of S-adenosylhomocysteine by LuxS in bacteria[8]
While several studies have looked at the role of QC by Isoleucyl-tRNA synthetase (IleRS) in E. coli, relatively few studies have examined the importance of QC in other organisms
As we had previously proposed that QC maybe more critical under conditions of stress that limit cellular growth[3], we chose to analyze the role of QC by IleRS in B. subtilis, which undergoes several distinct phenotypic or developmental shifts in response to starvation or slow growth, including the formation of environmentally-resistant endospores[24]
Summary
Required for Efficient Sporulation received: 11 October 2016 accepted: 22 December 2016. The loss of aminoacylation quality control in the ileS(T233P) strain resulted in the inability to compete with a wild-type strain under selective conditions that required sporulation. These data show that the quality control function of IleRS is required in B. subtilis for efficient sporulation and suggests that editing by aminoacyl-tRNA synthetases may be important for survival under starvation/nutrient limitation conditions. Beneficial is the higher level of mutations observed in colonies of E. coli IleRS QC-defective cells that are allowed to age; the full mechanism by which DNA mutations arise in response to loss of quality control is unknown[22]. The QC-defective IleRS strain was outcompeted by wild-type strains under conditions involving periodic sporulation and outgrowth, supporting a general role for quality control by aaRS under starvation or nutrient-limited conditions
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