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Unconventional initiator tRNAs sustain Escherichia coli

Samhita, Laasya and Shetty, Sunil and Varshney, Umesh (2012) Unconventional initiator tRNAs sustain Escherichia coli. In: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, 109 (32). pp. 13058-13063.

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Official URL: http://dx.doi.org/10.1073/pnas.1207868109


Of all tRNAs, initiator tRNA is unique in its ability to start protein synthesis by directly binding the ribosomal P-site. This ability is believed to derive from the almost universal presence of three consecutive G-C base (3G-C) pairs in the anticodon stem of initiator tRNA. Consistent with the hypothesis, a plasmid-borne initiator tRNA with one, two, or all 3G-C pairs mutated displays negligible initiation activity when tested in a WT Escherichia coli cell. Given this, the occurrence of unconventional initiator tRNAs lacking the 3G-C pairs, as in some species of Mycoplasma and Rhizobium, is puzzling. We resolve the puzzle by showing that the poor activity of unconventional initiator tRNAs in E. coli is because of competition from a large pool of the endogenous WT initiator tRNA (possessing the 3G-C pairs). We show that E. coli can be sustained on an initiator tRNA lacking the first and third G-C pairs; thereby reducing the 3G-C rule to a mere middle G-C requirement. Two general inferences following from our findings, that the activity of a mutant gene product may depend on its abundance in the cell relative to that of the WT, and that promiscuous initiation with elongator tRNAs has the potential to enhance phenotypic diversity without affecting genomic integrity, have been discussed.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to the National Academy of Sciences, USA
Keywords: fidelity of initiation;ribosome;phenotypic plasticity
Department/Centre: Division of Biological Sciences > Microbiology & Cell Biology
Depositing User: review EPrints Reviewer
Date Deposited: 20 Nov 2012 08:11
Last Modified: 20 Nov 2012 08:11
URI: http://eprints.iisc.ac.in/id/eprint/45172

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