Umesh Varshney

Microbiology and Cell Biology
Research Areas: 
Mycobacteria, DNA repair, protein synthesis
Research Highlights: 

We use E. coli and Mycobacteria as model systems to study mechanistic aspects of protein synthesis and DNA repair. The primary interest of the lab is to study mechanistic aspects of protein synthesis and DNA repair using E. coli and Mycobacteria as model systems. The lab has two main research groups : The Protein Synthesis Group and The DNA Repair Group. (i) Mechanism of ribosome recycling: Subsequent to the action of release factors at the step of termination, ribosomes remain bound to the mRNA in a post-termination complex. In eubacteria, the post-termination complexes are disassembled by the action of ribosome recycling factor (RRF) and elongation factor G (EFG). We have shown that specific interactions between RRF and EFG are essential to recycle the post-termination complexes. Such interactions between RRF and EFG are also required to recycle the stalled ribosomes (pre-termination ribosomal complexes) during the step of elongation by releasing peptidyl-tRNAs from them. The function of EFG in ribosome recycling is different from its classical role in translocation, and our recent observations suggest that a distinct set of interactions of EFG with RRF and the ribosome is crucial in this process. Further, we have shown that there is a functional interaction between RRF and IF3 in recycling of both the pre-, and post-termination ribosomal complexes. Present research is focused on the interplay of various factors during the various steps of protein synthesis. (ii) DNA repair in mycobacteria: Owing to their G+C rich genomes, mycobacteria are naturally at increased risk of cytosine deamination (to uracil), and oxidative damage to guanosine (to 8-oxoG). The uracil and 8-oxoG damages in DNA are repaired by Ung and Fpg, respectively. In addition, nucleotide excision repair (NER) is known to repair a broad spectrum of DNA damages. We have shown that the ung- strains of M. smegmatis exhibit increased mutator phenotype and poor endurance in mouse macrophages. Using M. smegmatis strains wherein fpg, mutY (encoding proteins involved in 8-oxoG repair) or uvrB (involved in NER pathway) genes have been inactivated, we have shown that the NER pathway is vital in protecting the organism from a variety of commonly encountered DNA damaging agents. Considering that in the host, the pathogen is subjected to various DNA damaging agents (RNI, ROS), a compromise in the DNA repair capacity could prove detrimental to the pathogen's existence. We are continuing our studies in DNA repair in M. tuberculosis with the aim to develop newer drug targets and also the attenuated strain as possible vaccine candidates.