ISOLATION AND PRELIMINARY CHARACTERISTICS OF EXTRACHROMOSOMAL ELEMENTS OF BACILLUS-THURINGIENSIS DNA

  • 1 January 1977
    • journal article
    • research article
    • Vol. 13  (3) , 496-+
Abstract
Centrifugation of B. thuringiensis 351 DNA in CsCl-ethidium bromide density gradient revealed, besides the main band of chromosomal DNA (.rho. [density] = 1.56 g/cm2), some additional bands with higher density, which usually correspond to circular superhelix DNA. Six discrete bands are observed under electrophoresis, which suggests that the preparation contains circular DNA of different size. Treatment with DNase results in the appearance of 3 bands corresponding to opened circular DNA, with MW of 12.106-4.106 daltons. Circular superhelix and opened circular DNA are found in minor fraction by EM. Statistical analysis revealed the presence of at least 3 types of circular molecules of different size. The variant 351-10, free of extrachromosomal elements, is isolated after ethidium bromide treatment at high temperature. Possible mechanisms of circular DNA formation are discussed. Biological function of extrachromosomal DNA fragments in B. thuringiensis is still obscure.