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Characterization of the dnaG locus in Mycobacterium smegmatis reveals linkage of DNA replication and cell division.

ABSTRACT: We have isolated a UV-induced temperature-sensitive mutant of Mycobacterium smegmatis that fails to grow at 42 degrees C and exhibits a filamentous phenotype following incubation at the nonpermissive temperature, reminiscent of a defect in cell division. Complementation of this mutant with an M. smegmatis genomic library and subsequent subcloning reveal that the defect lies within the M. smegmatis dnaG gene encoding DNA primase. Sequence analysis of the mutant dnaG allele reveals a substitution of proline for alanine at position 496. Thus, dnaG is an essential gene in M. smegmatis, and DNA replication and cell division are coupled processes in this species. Characterization of the sequences flanking the M. smegmatis dnaG gene shows that it is not part of the highly conserved macromolecular synthesis operon present in other eubacterial species but is part of an operon with a dgt gene encoding dGTPase. The organization of this operon is conserved in Mycobacterium tuberculosis and Mycobacterium leprae, suggesting that regulation of DNA replication, transcription, and translation may be coordinated differently in the mycobacteria than in other bacteria.

SUBMITTER: Klann AG

PROVIDER: S-EPMC106850 | biostudies-literature | 1998 Jan

REPOSITORIES: biostudies-literature

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Characterization of the dnaG locus in Mycobacterium smegmatis reveals linkage of DNA replication and cell division.

Klann A G AG Belanger A E AE Abanes-De Mello A A Lee J Y JY Hatfull G F GF

Journal of bacteriology 19980101 1

We have isolated a UV-induced temperature-sensitive mutant of Mycobacterium smegmatis that fails to grow at 42 degrees C and exhibits a filamentous phenotype following incubation at the nonpermissive temperature, reminiscent of a defect in cell division. Complementation of this mutant with an M. smegmatis genomic library and subsequent subcloning reveal that the defect lies within the M. smegmatis dnaG gene encoding DNA primase. Sequence analysis of the mutant dnaG allele reveals a substitution ...[more]

PMID: 9422594

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Project description:Mycobacterium smegmatis SigF is a group III sigma factor. Its ortholog in M. tuberculosis is reported to have role in regulation and function of cell wall components. In present study we have created an M. smegmatis M-NM-^TsigF mutant by allele exchange method. M. smegmatis sigF mutant shows non pigmented phenotype and is more sensitive to hydrogen peroxide generated oxidative stress. DNA microarray analysis of M. smegmatis wild type and M-NM-^TsigF mutant suggests that SigF in this species controls the expression of several energy and central intermediary metabolism genes along with regulation of carotenoid biosynthesis. Gene expression patterns of M.smegmatis wild type and M-NM-^TsigF mutant strains were compared at two growth stages i.e. log (OD600 ~1.4) and stationary (OD600 ~3.0). M. smegmatis strains were grown in DifcoTM MiddleBrook 7H9 broth base (BD Biosciences, Sparks, MD, USA) with 0.2% glycerol (v/v) and 0.05% Tween-80 (Sigma-Aldrich, St Louis, MO, USA) supplemented with 10% albumen dextrose catalase (BD Biosciences) (v/v) at 37 0C with continuous shaking. Total RNA was isolated using Trizole (Invitrogen) method and labelled with cyanine 3 (Cy3) as per Agilent 1-color labelling protocol (Version 5.5, February 2007). Six hundred nanograms of each Cy3 labelled samples were fragmented and hybridized. Fragmentation of labeled cRNA and hybridization were performed using Gene Expression Hybridization kit (Agilent Technologies). Hybridization was carried out in AgilentM-bM-^@M-^Ys Surehyb Chambers at 65 0C for 16 h. The hybridized slides were washed using Agilent Gene Expression wash buffers and scanned using the Agilent Microarray Scanner G Model G2565BA at 5 micron resolution. Feature extracted data was analysed using GeneSpring GX v 7.3.1 software from Agilent. Normalization of the data was done in GeneSpring GX using the recommended one color Per Chip and Per Gene Data Transformation. Set measurements less than 0.01 to 0.01 per chip, normalize to 50th percentile per gene, and normalize to specific samples.

Project description:Septation in bacteria requires coordinated regulation of cell wall biosynthesis and hydrolysis enzymes so that new septal cross-wall can be appropriately constructed without compromising the integrity of the existing cell wall. Bacteria with different modes of growth and different types of cell wall require different regulators to mediate cell growth and division processes. Mycobacteria have both a cell wall structure and a mode of growth that are distinct from well-studied model organisms and use several different regulatory mechanisms. Here, using Mycobacterium smegmatis, we identify and characterize homologs of the conserved cell division regulators FtsL and FtsB, and show that they appear to function similarly to their homologs in Escherichia coli We identify a number of previously undescribed septally localized factors which could be involved in cell wall regulation. One of these, SepIVA, has a DivIVA domain, is required for mycobacterial septation, and is localized to the septum and the intracellular membrane domain. We propose that SepIVA is a regulator of cell wall precursor enzymes that contribute to construction of the septal cross-wall, similar to the putative elongation function of the other mycobacterial DivIVA homolog, Wag31.IMPORTANCE The enzymes that build bacterial cell walls are essential for cell survival but can cause cell lysis if misregulated; thus, their regulators are also essential. The number and nature of these regulators is likely to vary in bacteria that grow in different ways. The mycobacteria are a genus that have a cell wall whose composition and construction vary greatly from those of well-studied model organisms. In this work, we identify and characterize some of the proteins that regulate the mycobacterial cell wall. We find that some of these regulators appear to be functionally conserved with their structural homologs in evolutionarily distant species such as Escherichia coli, but other proteins have critical regulatory functions that may be unique to the actinomycetes.

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Characterization of the dnaG locus in Mycobacterium smegmatis reveals linkage of DNA replication and cell division.

Publications

Characterization of the dnaG locus in Mycobacterium smegmatis reveals linkage of DNA replication and cell division.

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