Functional analysis of host-specificity mutants inEscherichia coli

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Abstract
Evidence from a functional analysis of host-specificity mutants in merodiploids is presented which supports the suggestion that three genes,hss, hsrandhsm, are necessary for the expression of host-controlled restriction and modification. The host-specificity phenotype expressed by the merodiploids provides evidence that at least two genes,hssandhsr, are concerned in the expression of host-specific restriction of DNA and one of these genes,hss, is responsible for the strain specificity of the restriction enzyme. A class of modification-deficient mutants isolated from restriction-deficient, modification-proficient mutants, was also tested for complementation in merodiploids and the phenotype of these merodiploids provides evidence that at least two genes,hssandhsm, are concerned in the expression of host-specific modification of DNA and one of these genes,hss, is responsible for the strain specificity of the modification enzyme. How these three genes function at the molecular level is discussed in terms of models based on the interaction of subunits to form oligomeric enzymes.