Mutant varieties not nonfunctional
doi:10.1038/nindia.2012.109 Published online 8 August 2012
Fresh research on the genetics of gut bacteria Escherichia coli has dispelled the long held notion that its survival is dependent on three G-C base pairs in its initiator tRNA. Through mutant varieties, the researchers prove that this is not the case — E.coli can survive even with just one of those G-C pairs. The researchers suggest the need for caution in dismissing mutants as 'nonfunctional'.
Of all tRNAs known, the initiator tRNA is unique since it starts protein synthesis by directly binding to the ribosomal P-site. This ability is believed to be due to the three consecutive G-C base pairs in the anticodon stem of initiator tRNA.
However, in some species such as Mycoplasma and Rhizobium, these initiator tRNAs lack the 3G-C pairs. The researchers sought to resolve this puzzle and found that the poor activity of initiator tRNAs in E. coli was because of the competition from a large pool of endogenous wild-type initiator tRNA (possessing the 3G-C pairs).
They showed that E. coli could 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. Thus they prove 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.
The authors of this work are from: Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore, India.
- Samhita, L. et al. Unconventional initiator tRNAs sustain Escherichia coli. P. Natl. Acad. Sci USA 109, 13058-13063 (2012) | Article |