title: Stabilization of the primary sigma factor of Staphylococcus aureus by core RNA polymerase.
abstract: The primary sigma factor (sigma(A)) of Staphylococcus aureus, a potential drug target, was little investigated at the structural level. Using an N-terminal histidine-tagged sigma(A) (His-sigma(A)), here we have demonstrated that it exits as a monomer in solution, possesses multiple domains, harbors primarily alpha-helix and efficiently binds to a S. aureus promoter DNA in the presence of core RNA polymerase. While both N- and C-terminal ends of His- sigma(A) are flexible in nature, two Trp residues in its DNA binding region are buried. Upon increasing the incubation temperature from 25 degrees to 40 degrees C, 60% of the input His-sigma(A) was cleaved by thermolysin. Aggregation of His-sigma(A) was also initiated rapidly at 45( degrees )C. From the equilibrium unfolding experiment, the Gibbs free energy of stabilization of His-sigma(A) was estimated to be +0.70 kcal mol(-1). The data together suggest that primary sigma factor of S. aureus is an unstable protein. Core RNA polymerase however stabilized sigma(A) appreciably.
authors.affiliation: Department of Biochemistry, Bose Institute, Kolkata, India.
authors.forename: Rajkrishna
authors.initials: R
authors.lastname: Mondal
authors.forename: Tridib
authors.initials: T
authors.lastname: Ganguly
authors.forename: Palas K
authors.initials: PK
authors.lastname: Chanda
authors.forename: Amitava
authors.initials: A
authors.lastname: Bandhu
authors.forename: Biswanath
authors.initials: B
authors.lastname: Jana
authors.forename: Keya
authors.initials: K
authors.lastname: Sau
authors.forename: Chia Y
authors.initials: CY
authors.lastname: Lee
authors.forename: Subrata
authors.initials: S
authors.lastname: Sau
mesh_terms: D012321:DNA-Directed RNA Polymerases / Q000378:metabolism*; D055550:Protein Stability; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000378:metabolism*
chemical_list: D011994:Recombinant Proteins; D012808:Sigma Factor; D012321:DNA-Directed RNA Polymerases