Alteration of the specificity of Pst I restriction endonuclease

The influence of factors on the substrate-specificity of Pst I restriction endonuclease has been studied with the method of electrophoresis. The results show that, the specificity of Pst I almost can not be influenced by the single alteration of the concentration of Tris·HCl, Mg2+ or Na+ in the reaction system, but it can be altered by the reduction of any two of them. The specificity can not be altered by the single alteration of pH or the replacement of Mg2+ with Mn2+. The addition of glycerol or dimethylsulphoxide (DM-SO) to the reaction system results in the relaxation of the substrate-specificity of Pst I, but dimethyl-methylformide, glycol and ethyl alcohol can not bring about the alteration of Pst I specificity. Through the method of cloning and sequencing, the nucleotides of No. 1 and 6 in the recognition sequence of Pst I have changed (1C-&gtA or 6G-&gtT). Used with the enzyme analysis of an artificially synthetic DNA segment containing a special sequence, the nucleotides of No. 1 and 6 have both changed (1C-&gtA and 6G-&gtT). The recognition sequence of Pst I is speculated to be changed from CTGCA[Arrow Down]G to TGCA[Arrow Down].