Pyrimidine dimer-induced enhancement of recombination among lambda bacteriophages

Regulation of toxinogenesis in Corynebacterium diphtheriae. II. Genetic mapping of a tox regulatory mutation in bacteriophage beta

The structural gene for diphtherial toxin is present in corynebacteriophage beta. Previous studies located several point mutations within the tox locus and determined the orientation of transcription of the toxin structural gene. The production of maximal quantities of toxin by Corynebacterium diphtheriae C7(beta) occurs only when the bacteria are iron deficient. Mutations in phage beta can affect this control of toxin production by iron. The tox-201 mutation regulates expression of the toxin structural gene in a cis-dominant manner and permits large amounts of toxin to be made under high-iron conditions when phage beta tox-201 infects C. diphtheriae C7. In this study tox-201 was found to be closely linked to the structural gene for toxin. We performed a series of multifactor matings to determine the relative positions of tox-201 and several point mutations within the toxin structural gene. The order of these markers on the vegetative genetic map of phage beta was tox-201-tox-4-tox-2-tox-30. These findings establish that the tox-201 regulatory site is closely linked to the end of the toxin structural gene corresponding to the origin of transcription. This location is consistent with our hypothesis that tox-201 defines a cis-dominant regulatory element, such as an operator, promoter, or attenuator, involved in control of toxinogenesis in C. diphtheriae C7(beta).

Mapping missense and nonsense mutation in gene cI of bacteriophage lambda: marker effects

Amber and missense mutations in gene cI of bacteriophage lambda were mapped by reciprocal four-factor crosses, selecting recombinants between the outside markers (N amber and O amber). Distances between cI missense mutations were additive. Several cI amber mutants recombined with other cI mutations with a higher frequency than expected from the map location. Multiple exchanges in the N-O region occurred at a frequency greater than expected by chance. This "high negative interference" was especially marked in crosses with the cI amber mutations that were strong recombiners. A new ind mutation, ind2, was found near tsU51, to the left of the previously-known ind1 mutation, which is located almost in the center of gene cI. The mutation c50 maps to the right of tsU50 and c71. Mutations c60, and ts71, which differ in phenotype, are apparently at the same site.

Characterization and genetic mapping of nontoxinogenic (tox) mutants of corynebacteriophage beta

Seven new nontoxinogenic (tox) mutants of corynebacteriophage beta were isolated. Strains of Cornyebacterium diphtheriae C 7 lysogenic for these tox mutants of beta were tested for their ability to produce extracellular diphtherial toxin or proteins (CRMs) that cross-react immunologically with toxin. By using a sensitive reversed passive hemagglutination assay for toxin antigen, three of the tox mutants were phenotypically CRM+ and four were CRM-. The molecular weights of the CRMs produced by mutants beta tox-1, beta tox-2, and beta tox-3 were determined to be approximately 20,000, 26,000, and 34,000, respectively, by electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. The 26,000 and 34,000-dalton CRMs had nicotinamide adenine dinucleotide: elongation factor 2 adenosine diphosphate ribose transferase activity, but the 20,000-dalton CRM did not. These three CRMs correspond to amino-terminal fragments of diphtherial toxin and appear to be formed by chain termination during protein synthesis directed by phages with nonsense mutations in the structural gene for diphtherial toxin. No complementation was observed between independently isolated tox mutants of phage beta. The positions of four tox markers on the vegetative genetic map of phage beta were determined, and the orientation of transcription of the structural gene for diphtherial toxin with respect to other markers on the genetic map of phage beta was established.