The eco72IC gene specifies a trans-acting factor which influences expression of both DNA methyltransferase and endonuclease from the Eco72I restriction-modification system

Eco72I from Escherichia coli RFL72 is a type-II restriction-modification (R-M) system recognizing and cleaving the sequence 5′-CAC↓GTG-3′. The R-M genes are transcribed divergently and between the two genes is a small open reading frame codirectional to the R gene. This small ORF acts both to stimulate ENase expression and to depress DNA methyltransferase synthesis. The activity of βGal produced from the eco72IM::lacZ translational fusion increased tenfold, and eco72IR::lacZ translational fusion βGal activity decreased 130-fold when eco72IC was inactivated by a frameshift mutation. Analysis of nucleotide sequences of R-M systems, containing C genes, revealed a 5′-ACCTTATAGTC-3′ consensus sequence upstream from the regulatory genes in all six analysed R-M systems. This sequence, named C-box, may play the role of an operator sequence.