[Characteristics of the mutants of the temporate actinophage phiC31 with a disordered lysogenicity and that overcome the immunity of lysogenic cultures].

The study of c- and cts-mutants of the temperate actinophage phiC31, affecting the lysogenization process in Streptomyces coelicolor showed the interallelic negative complementation. This fact implies the protein nature of the repressor synthesized under the control of gene C and its multiunit structure. Transdominant c- and cts-mutants were partly virulent being able to overcome the immunity of lysogens with effecting of plating (eop) about 5. Virulent mutants infecting lysogens with an eop 1 were detected. Differences in behaviour of virulent mutants isolated from transdominant mutant (v) stock and those containing a recessive mutation in the gene C (vd- and vdt-mutants) are shown. It is demonstrated that vd-mutants unlike v-mutants are not capable of growing without phage-helper (presumably prophage) and use many prophage gene products marked by ts- and host-range-mutations to form progeny. Common to all isolated virulent mutants are their ability to promote the prophage induction in lysogens and inability to display virulent phenotype in the absence of a mutation in the gene C.