Due to the intensive studies on the molecular biology of E. coli and its genetic elements, the dawn of genetic engineering was determined by using it as the host of choice in cloning experiments (Glass, 1982). Using this microorganisms, several laboratories are involved in works targeted to the construction and cloning of complex recombinant molecules able to transform other microbial hosts for different economic goals (Brent and Irwin 1987). The present~'work aimed to transform the ~. coli strain K12 JM 109 using the previously constructed recombinant plasmid p UC18 , which contains the sequence of gene "C'I belonging to the Rhizobiophage 11 (Abdel-Sabour, 1989). This cloning experiment represents an important step in further trials to construct more complex recombinant plasmids able to transform Rhizobia.