[Modification of the modification-restriction system in staphylococci].
A new system of host specificity of DNA, called Sau67 according to the available nomenclature, was identified in Staphylococcus aureus 6782 strain by means of cross titration with staphylophage 729 considering that the phage exhibited the highly effective absorption properties. A total preparation of Sau67 methylases was isolated using ammonium sulfate fractionation. The enzyme preparation contained methylases of cytosine and adenine, where the activity of adenine methylases constituted only for 5% of the total methylase activity. As shown by kinetics of methylation low content of unspecific cellular nucleases was found in the St. aureus 6782 strain; these reasons are important for isolation of restricting endonucleases containing in the strain. 100 micrograms of protein of the total enzymatic fraction enabled to methylate the acceptory DNA at the maximal rate within 1.5 hr of incubation in phosphate buffer, pH 7.9. The fraction of cytosine methylases free of adenine methylating activity was obtained after chromatography on Sepharose blue with NaCl concentration stepwise gradient.