title: An IPTG Inducible Conditional Expression System for Mycobacteria.
abstract: Conditional expression strains serve as a valuable tool to study the essentiality and to establish the vulnerability of a target under investigation in a drug discovery program. While essentiality implies an absolute requirement of a target function, vulnerability provides valuable information on the extent to which a target function needs to be depleted to achieve bacterial growth inhibition followed by cell death. The critical feature of an ideal conditional expression system is its ability to tightly regulate gene expression to achieve the full spectrum spanning from a high level of expression in order to support growth and near zero level of expression to mimic conditions of gene knockout. A number of bacterial conditional expression systems have been reported for use in mycobacteria. The utility of an isopropylthiogalactoside (IPTG) inducible system in mycobacteria has been reported for protein overexpression and anti-sense gene expression from a replicating multi-copy plasmid. Herein, we report the development of a versatile set of non-replicating IPTG inducible vectors for mycobacteria which can be used for generation of conditional expression strains through homologous recombination. The role of a single lac operator versus a double lac operator to regulate gene expression was evaluated by monitoring the expression levels of β-galactosidase in Mycobacterium smegmatis. These studies indicated a significant level of leaky expression from the vector with a single lac operator but none from the vector with double lac operator. The significance of the double lac operator vector for target validation was established by monitoring the growth kinetics of an inhA, a rpoB and a ftsZ conditional expression strain grown in the presence of different concentrations of IPTG. The utility of this inducible system in identifying target specific inhibitors was established by screening a focussed library of small molecules using an inhA and a rpoB conditional expression strain.
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Sudha
authors.initials: S
authors.lastname: Ravishankar
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Anisha
authors.initials: A
authors.lastname: Ambady
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Haripriya
authors.initials: H
authors.lastname: Ramu
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Naina Vinay
authors.initials: NV
authors.lastname: Mudugal
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Ragadeepthi
authors.initials: R
authors.lastname: Tunduguru
authors.affiliation: School of Biosciences & Technology, VIT University, Vellore, Tamil Nadu, India.
authors.forename: Anand
authors.initials: A
authors.lastname: Anbarasu
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Umender K
authors.initials: UK
authors.lastname: Sharma
authors.affiliation: AstraZeneca India Pvt Ltd, Bellary Road, Hebbal, Bengaluru, Karnataka, India.
authors.forename: Vasan K
authors.initials: VK
authors.lastname: Sambandamurthy
authors.affiliation: School of Biosciences & Technology, VIT University, Vellore, Tamil Nadu, India.
authors.forename: Sudha
authors.initials: S
authors.lastname: Ramaiah
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology*; D007763:Lac Operon / Q000235:genetics; D020102:Mycobacterium smegmatis / Q000254:growth & development / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010641:Phenotype; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003598:Cytoskeletal Proteins; C071525:FtsZ protein, Bacteria; D007544:Isopropyl Thiogalactoside; D010088:Oxidoreductases; C085257:InhA protein, Mycobacterium; D001616:beta-Galactosidase