Evidence of horizontal transfer of the EcoO109I restriction-modification gene to Escherichia coli chromosomal DNA

A DNA fragment carrying the genes coding for EcoO109I endonuclease and EcoO 109I methylase, which recognize the nucleotide sequence 5'-(A/G)GGNCC(C/T)- 3', was cloned from the chromosomal DNA of Escherichia coil H709c. The EcoO 109I restriction-modification (R-R;I) system was found to be inserted betwe en the int and psu genes from satellite bacteriophage P4, which were lysoge nized in the chromosome at the P4 phage attachment site of the correspondin g leuX gene observed in E. coil K-12 chromosomal DNA. The sid gene of the p rophage was inactivated by insertion of one copy of IS21. These findings ma y shed light on the horizontal transfer and stable maintenance of the R-M s ystem.