Two DNA methylases (DNAmets) can be separated through the cell cycle. The first appears as a minor peak in G1, the second as a major peak in S. Both enzymes protect from Hpall a plasmid (H31), constructed with the pBR322 vector (4.3 kbp) and the inverted Aγ, fragment of the human globin gene (3.5 kbp), inserted at its HindIII site (the vector carries several HpaII sites, the insert only one HpaII site). DNAmets G1 and S show distinct K m values and different kinetics vs the ionic strength of the medium, while their Michaelis-Menten and Lineweaver-Burk plots are sigmoidal and hyperbolical curves, respectively. This is the first suggestion about the allosteric nature of the eukaryotic DNAmet system.
