Enhanced recovery of rII mutations in the absence of selection in a ligase-negative mutant of bacteriophage T 4

Isolation of bacteriophage T4 DNA polymerase mutator mutants

More than 20 new bacteriophage T4 DNA polymerase mutants have been isolated by a procedure designed to select mutants with high spontaneous mutation rates. Some of the mutants produce the highest mutation frequencies that have been observed in T4 thus far. The design of the selection procedure allows for the isolation of mutator mutants that preferentially induce certain types of replication errors, and some of the mutator mutants have mutational specificities different from wild-type. The new mutants are clustered at just two sites in the DNA polymerase gene, and this result confirms an earlier observation.

Mutator and antimutator phenotypes of suppressed amber mutants in genes 32, 41, 44, 45, and 62 in bacteriophage T4

Bacteriophage T4 genes 32, 41, 44, 45, 56, and 62 are essential to DNA replication. Amber mutants (suppressed by su+1, su+2, or su+3 bacteria) in these genes were examined for any mutator or antimutator effects on the reversion of a transition mutation. In every case except for mutations in gene 56, elevated or lowered error frequencies were observed. These results indicate the importance of all of the replicative proteins in the determination of error frequency.

The dependence of HNO2 mutagenesis in phage T4 on ligase and the lack of dependence of 2AP mutagenesis on repair functions

A temperature sensitive ligase allele of phage T4 reduced or eliminated HNO2 induced reversion of am mutants. Since at the temperatures used, the ligase mutant is defective in the repair of some types of lethal lesions (i.e., UV, MMS and EMS induced lesions) these results indicate that HNO2 mutagenesis may occur through a ligase dependent repair pathway. In contrast, 2AP induced mutation was not inhibited by mutants defective in the gene 30 ligase or in genes 32, 39, 41, 42, 44, 45, 46, 47, 49, 52, 56, 58-61 and v. This indicates that 2AP mutagenesis probably does not depend on a repair pathway in phage T4.

Induction of error-prone repair as a consequence of DNA ligase deficiency in Escherichia coli

DNA ligase deficiency is shown to induce generalized mutator activity in E. coli. This mutator activity is unaffected by 3 mug/ml of chloramphenicol but is abolished both in lig-recA double mutants and by incubation with 20 mug/ml of chloramphenicol. Dna ligase deficiency is also shown to reactivate ultraviolet light-irradiated phage lambda and T7 and to increase both spontaneous and ultraviolet light-induced mutagenesis in phage lambda, all of which are abolished in lig-recA strains. Interaction occurs between the molecular events of mutagenesis induced by ultraviolet irradiation and those induced by DNA ligase deficiency. These observations suggest a common pathway, coordinately expressed with the inducible repair mode, that is responsible for mutagenesis.

Effects of p-fluorophenylalanine on the induction of mutations in bacteriophage T4. II. Nitrous acid mutagenesis

The effects of rho-fluorophenyalanine (PFPA), an analogue of phenylalanine (PHE), on the potency and the specificity of nitrous acid (NA) mutagenesis in the gamma system of bacteriophage T4 were measured. (a) Forward mutation. THE frequencies of NA-induced gamma mutants were approximately doubled when mutagenized phage infected E. coli B in the presence of the analogue compared to controls where PHE was substituted for PFPA, or where no amino acid was added. The spontaneous forward mutation frequency was not affected by the analogue, nor was the specificity of the NA mutagenesis. (b) Reverse mutation. The frequency of spontaneous and NA-induced reversion of an gammaII transition mutant was unaffected by PFPA if the phage were plated direct on the restrictive growth in the presence of PFPA the induced reversion frequency was increased about 3-fold compared to the control.