[Restriction of two-replicon shuttle Escherichia coli-Streptomyces plasmids in Streptomyces lividans strain 66]

The shuttle Escherichia coli - Streptomyces plasmids were used to transform S. lividans 66. Plasmid DNAs isolated from this strain transform it 10-1000-fold more efficiently than DNAs from E. coli. Rare transformant cured from most restricted plasmid is more efficient recipient of plasmid DNA from E. coli and has the property of R +/- M+ mutant. Restriction in S. lividans 66 correlates with the appearance in DNA from E. coli of the sites susceptible to Scg2I restriction endonuclease. The latter was isolated earlier from recombinant strain Rcg2, a hybrid between S. griseus Kr. 15 and S. coelicolor A3(2). Scg2I possesses the recognition sequence CCTAGG, like EcoRII, MvaI and Eco dcm methylase. The DNA resistant to Scg2I cleavage retained this ability after in vitro modification by EcoRII methylase. So, the resistance of DNA to Scg2I cleavage is not connected with methylation at 4th and 5th position of second cytosine in the recognition sequence. Neither restriction of plasmid DNA in S. lividans 66 is dependent on dcm modification in E. coli, though its dependence on dam modification is not excluded. It is assumed that the restriction in S. lividans 66 is specified by endonuclease analogous to Scg2I.