Reduction in DNA topoisomerase I level affects growth, phenotype and nucleoid architecture of Mycobacterium smegmatis

Ahmed, Wareed and Menon, Shruti and Karthik, Pullela V and Nagaraja, Valakunja (2015) Reduction in DNA topoisomerase I level affects growth, phenotype and nucleoid architecture of Mycobacterium smegmatis. In: MICROBIOLOGY-SGM, 161 (2). pp. 341-353.

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Abstract

The steady-state negative supercoiling of eubacterial genomes is maintained by the action of DNA topoisomerases. Topoisomerase distribution varies in different species of mycobacteria. While Mycobacterium tuberculosis (Mtb) contains a single type I (Topol) and a single type II (Gyrase) enzyme, Mycobacterium smegmatis (Msm) and other members harbour additional relaxases. Topol is essential for Mtb survival. However, the necessity of Topol or other relaxases in Msm has not been investigated. To recognize the importance of Topol for growth, physiology and gene expression of Msm, we have developed a conditional knock-down strain of Topol in Msm. The Topol-depleted strain exhibited extremely slow growth and drastic changes in phenotypic characteristics. The cessation of growth indicates the essential requirement of the enzyme for the organism in spite of having additional DNA relaxation enzymes in the cell. Notably, the imbalance in Topol level led to the altered expression of topology modulatory proteins, resulting in a diffused nucleoid architecture. Proteomic and transcript analysis of the mutant indicated reduced expression of the genes involved in central metabolic pathways and core DNA transaction processes. RNA polymerase (RNAP) distribution on the transcription units was affected in the Topol-depleted cells, suggesting global alteration in transcription. The study thus highlights the essential requirement of Topol in the maintenance of cellular phenotype, growth characteristics and gene expression in mycobacteria. A decrease in Topol level led to altered RNAP occupancy and impaired transcription elongation, causing severe downstream effects.

Item Type:	Journal Article
Publication:	MICROBIOLOGY-SGM
Publisher:	SOC GENERAL MICROBIOLOGY
Additional Information:	Copy right for this article belongs to the SOC GENERAL MICROBIOLOGY, MARLBOROUGH HOUSE, BASINGSTOKE RD, SPENCERS WOODS, READING RG7 1AG, BERKS, ENGLAND
Department/Centre:	Division of Biological Sciences > Microbiology & Cell Biology
Date Deposited:	31 Jul 2015 13:44
Last Modified:	31 Jul 2015 13:44
URI:	http://eprints.iisc.ac.in/id/eprint/51965

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