E.coli strain W (ATCC 9637) is lysogenic for 2 phages which propagate on either E.coli C or E.coli K12. Each phage adsorbs specifically to only one of these hosts and the phages are therefore designated W0 and Wk respectively. These phages display a large number of similarities to phage Mu but restriction endonuclease digestion and probing with radioactively labelled DNA show that the W-phage are not identical to phage Mu.
Lysogens of E.coli C carrying either of the W-phage exhibit strong restriction towards phages P, and Lambda; lysogens of E.coli K12 carrying the same phage have not been shown to exhibit such restriction.
Conjugation experiments between E.coli W, E.coli C, and E.coli K12 allowed the mapping of the insertion sites of the 2 W-prophages on the E.coli W genome