Research Summary

Stress dependent evolution in bacteria through manipulation of tRNA levels

Bacteria adapt to stress in various ways.  Recent work indicates that one such way is by the generation of novel translational products not encoded in conventional reading frames. I propose to test the hypothesis that tRNAs mediate a non genetic stress response by generating proteome diversity through (i) mis-initiation and (ii) misacylation. Bacterial cells show changes in the levels of charged tRNAs under stresses like amino acid starvation. I hypothesize based on previous results that mutant strains depleted of initiator tRNAs will show translation initiation at alternate sites along mRNAs and at non-AUG codons, potentially using amino acids other than methionine. Misacylation and misincorporation frequency will also be examined in wild type E.coli and mutant strains under different stress regimes. While in the short term, an altered proteome may help tide over a stress, prolonged maintenance of the stress could lead to the evolution of new traits via genetic changes that consistently produce the novel beneficial peptide(s). Alternatively, under weak or inconsistent stress, diverse phenotypes may arise but not be genetically fixed (~canalized). While canalization of a new phenotype may occur with rarely encountered and long term stresses, retaining the ability to explore many phenotypes (without canalization) could serve as an adaptation to survival in changing environments.

Figure Legend: Investigating the potential adaptive value of tRNA mediated translation errors in the bacterium E. coli