[System of host specificity and the DNA methylases of shigellae and their phages].

In Shigella sonnei cells there is a host DNA specificity system responsible for modification and restriction of DDII phage. DNA methylase from Shigella stutzeri cells is specific for adenine and catalyses the appearance of 6-'-methylaminopurine in the acceptory DNA. Methylases from Shigella sonnei cells are specific for adenine and cytosine and provide for the presence of 6'-methylaminopurine and 5'-methylcytosine in DNA. The modifying activity of these cells may be equally likely associated with both the enzymes. A simplified version of the additional methylation test has been developed for the study of enzyme specificity. The results of additional and cross methylation suggest that several adenine methylases are present in the cells of these Shigella, one of these enzymes being shared by Shigella stutzeri and Shigella sonnei. The DNA's isolated from Shigella sonnei and Shigella stutzeri cells are undermethylated and in vitro undergo additional methylation upon incubation with the appropriate enzyme.