본 논문에서는 Providencia stuartii 164 균주로부터 Pst I methylase를 분리하여 특성을 관찰하였다. 분리 방법으로는 $(NH_4)_2SO_4$ 분획법, DEAE-Cellulose 크로마토그라피법, Phosphocellulose 크로마토그라피법, 그리고 Heparin agarose 크로마토그라피법을 순서적으로 사용했다. 분리된 효소는 site-specific한 methylase였는데, 이것은 Pst I 제한효소로 자른 pBR322 DNA는 분리한 methylase에 의해 methylation이 일어나지 않은 사실과 분리한 methylase로 methylation 시킨 pBR322 DNA는 Pst I 제한효소로 잘라지지 않는다는 사실로 확인되었다. 또한 Pst I restriction-modification 유전자를 가지는 plasmid인 pRL829 DNA가 이 효소에 의해 더 이상 methylation이 일어나지 않은 사실은 분리해 낸 효소가 Pst I methylase임을 확신시켜 주었다. 이 효소는 pH 7.5에 서 가장 높은 활성도를 보여 주었고 50 mM 농도의 NaCl이 있으면 활성도가 증가했다. 또한 Pst I methylase는 외가닥으로 된 ${Phi}X$ 174 DNA를 잘 methylation 시키는 것으로 나타났다.
In this report, the purification and characterization of Pst I methylase from Providencia stuartii 164 strain was described. Pst I methylase was purified by the following procedures; ammonium sulfate fractionation, DEAE-cellulose chromatography, Phosphocellulose chromatography and Heparin agarose chromatography. Pst I methylase was a site-specific methylase which has been proven by the facts that pBR322 DNA cleaved by Pst I restriction endonuclease was not methylated by Pst I methylase, and pBR322 DNA methylated by Pst I methylase was not cleaved by Pst I restriction endonuclease. The plasmid pRL829, which contains Pst I restriction-modification genes and thus was fully methylated in vivo, was not methylated by Pst I methylase. These results strongly suggest that the methylase has a site specificity on Pst I recognition site. Pst I methylase activity has optima at pH 7.5 and in the presence of 50 mM NaCl. In addition, Pst I methylase has also been found to have methylation activity on single-strand ${Phi}X174$ DNA.
