Genetic studies on site-specific endodeoxyribonucleases in Bacillus subtilis: multiple modification and restriction systems in transformants of Bacillus subtilis 168

Summary We transformed B. subtilis 168 with DNA from B. subtilis IAM1231, IAM1192 and ATCC6633. When we examined the restriction activities of the transformants in vivo and in vitro using phage 105C we found the following: (1) Cells of either IAM1231 or IAM1192 have two modification and restriction systems (Bsu1231(1)-system and Bsu1231(II)-system in IAM1231, and Bsu1192(I)-system and Bsu1192(II)-systems in IAM1192), and cells of ATCC6633 have only one system (Bsu6633-system). (2) The restriction enzymes of all of these five systems are site-specific endonucleases. (3) The nucleotide sequence specificities of the enzymes involved in Bsu1231(I)-system, Bsu1192(I)-system and Bsu6633-system are the same; and those of Bsu1231(II)-system and Bsu1192(II)-system are the same. The sequence specificities of these two groups are different from each other and also different from those of the Bsu168-system of B. subtilis 168, the BsuR-system of B. subtilis R and the Bsu1247(I)-and Bsu1247(II)-systems which are systems of B. subtilis IAM1247. (4) Transformants possessing four different modification and restriction systems (Bsu1231(I)-, Bsu1247(I)-, BsuR- and Bsu168-systems) were constructed. (5) Transformation of two derivatives of 168 that were m _R ⁺ r _R ⁺ by DNA from IAM1231 produced 16 transformants that had the Bsu1231(II) restriction system, but had lost the BsuR system. Transformation of a derivative of 168 that was m _1247(II) ⁺ r _1247(II) ⁺ by DNA from m _1231(II) ⁺ r _1231(II) ⁺ -or m _R ⁺ r _R ⁺ -derivative of 168 produced about 100 each of transformants that had the Bsu1231(II)-restriction system or the BsuR-restriction system. But all these transformants lost the Bsu1247(II)-system.