Isolation and properties of a thermostable restriction endonuclease (ENDO R-Bst1503)

Abstract

A restriction endonuclease was isolated from Bacillus stearothermophilus 1503-4R (Bst1503) and purified to homogeneity. The enzyme required Mg2+ as a cofactor. Bst1503 exhibited maximal activity between pH 7.5-8.0, between 60.degree.-65.degree. C and with .apprx. 0.2 mM Mg2+. Bst1503 was not inactivated after exposure at 55.degree. or 65.degree. C for up to 10 h. After 2 h of incubation at 70.degree. C, Bst1503 was inactivated by 65%. Bst1503 was rapidly inactivated at 75.degree. C. A single protein-staining band having a MW of 46,000 was observed when Bst1503 was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme existed in 2 active forms, the predominating form with an S value of 8.3 (180,000) and the 2nd form with an S value of 5.4 (96,000). No conversion between the 8.3S and 5.4S forms was observed after storage. Bst1503 recognized 6 sites in [phage] TP-1C DNA, 1 site in [plasmid] pSC101 and sv-40 DNAs and 3 sites in [phage] .lambda.vir DNA. Bst1503 and BamHI [from Bacillus amyloliquefaciens] were isoschizomers. The effect of temperatures on the activity and stability of BamHI was determined.