[Coding R.M.EcoR1-plasmids derived from R-factor].

Bacteriophages P1vir and Mu-1 have been used for transductional shortening of recombinant R factor coding for R.M.EcoR1 isolated by Yoshimori et al. P1 shortening made possible the isolation of transmissive isogenic plasmids coding R.M.EcoR1 and differing in antibiotic resistances, as well as isolation of plasmids differing only in R.M.EcoR1 genes. Mu-1 mediated shortening favoured the isolation of transmissive R plasmids having lost the resistance to chloramphenicol but having all other markers of recombinant R factor intact. The data are interpreted in support of Yoshimori et al. supposition concerning the existence of R.M.EcoR1 coding recombinant R factor of Escherichia coli.