Lactose plasmid로 host chromosome에 도입시킨 S. lactis $KB_{21}$으로부터 spontaneous mutant와 자외선 처리로 lactose constutive mutant를 분리하였다. lactobionate를 탄소원으로 하는 배지에서 parent는 거의 생육하지 못하는 반면 mutant는 빠를 생육을 보임으로써 lactose constitutive mutant임을 확인하였다. Mutant의 $phospho-{eta}-galactosidase$ activity는 parent의 약 $1.7{sim}3.4$배를 나타내었다.
From S. lactis $KB_{21}$, stabilized strain by intergration of the lactose plasmid into the host chromosome, several lactose constitutive mutants were obtained by UV irradiation and spontaneous mutation. The rapid growth of the mutants in the medium containing lactobionate confirmed their constitutive nature. The mutants synthesized $phospho-{eta}-galactosidase$ with an activity of 1.7 to 3.4 times that of the parent.
