MsDpo4—a DinB Homolog fromMycobacterium smegmatis—Is an Error-Prone DNA Polymerase That Can Promote G:T and T:G Mismatches

Amit Sharma,Deepak T Nair

doi:10.1155/2012/285481

Amit Sharma, Deepak T Nair

Open Access

https://doi.org/10.1155/2012/285481

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Abstract

Error-prone DNA synthesis in prokaryotes imparts plasticity to the genome to allow for evolution in unfavorable environmental conditions, and this phenomenon is termed adaptive mutagenesis. At a molecular level, adaptive mutagenesis is mediated by upregulating the expression of specialized error-prone DNA polymerases that generally belong to the Y-family, such as the polypeptide product of the dinB gene in case of E. coli. However, unlike E. coli, it has been seen that expression of the homologs of dinB in Mycobacterium tuberculosis are not upregulated under conditions of stress. These studies suggest that DinB homologs in Mycobacteria might not be able to promote mismatches and participate in adaptive mutagenesis. We show that a representative homolog from Mycobacterium smegmatis (MsDpo4) can carry out template-dependent nucleotide incorporation and therefore is a DNA polymerase. In addition, it is seen that MsDpo4 is also capable of misincorporation with a significant ability to promote G:T and T:G mismatches. The frequency of misincorporation for these two mismatches is similar to that exhibited by archaeal and prokaryotic homologs. Overall, our data show that MsDpo4 has the capacity to facilitate transition mutations and can potentially impart plasticity to the genome.

Highlights

For proper cellular functioning, the integrity of the genome has to be maintained and it is essential that replication should be error free
This study showed that there was no increase in the frequency of mutations when these homologs were expressed ectopically in Mycobacterium smegmatis (Msm), and the authors suggest that mycobacterial DinB homologs function differently from those in other bacteria
We demonstrate that the polypeptide product of msmeg 1014 is a DNA polymerase

Summary

Introduction

The integrity of the genome has to be maintained and it is essential that replication should be error free. Studies in the past decade on prokaryotes have shown that in an adverse environment, adaptive mutagenesis is mediated by expression of error-prone DNA polymerases [3, 7] These specialized DNA polymerases, usually classified in the Yfamily, appear to possess distinct active sites that allow them to accommodate non-Watson-Crick base pairs and promote mismatches [8, 9]. These enzymes generally exhibit low fidelity and low processivity, and these properties are exploited to facilitate adaptive mutagenesis

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