Ultraviolet Induction of Chromosome Transfer by Autonomous Sex Factors in Escherichia coli

Abstract

K 12 bacteria, carrying an autonomous F factor or an F-prime factor, enhances the fertility of the population by increasing the number of cells which can transfer the bacterial chromosome. In contrast, under similar conditions the fertility of irradiated Hfr populations falls in proportion to the survivors. Following irradiation, the effect begins to develop after about 30 min. incubation in broth at 37", reaches a peak at about 90 min., and thereafter slowly declines. The effect develops with similar kinetics during post-irradiation incubation in minimal medium as in broth, provided the bacteria have been minimal-grown; in the case of broth-grown cells, appearance of the effect in minimal medium is greatly delayed. A comparison of the kinetics of the effect with the growth of the population as a whole shows that the u.v.-induced donor state is not inheritable. Mitomycin C, which resembles U.V. radiation in producing DNA damage repairable by a mechanism involving excision of single-stranded fragments, also induces new donor bacteria. Other agents such as X-rays and methyl methansulphonate (MMS) do not stimulate the production of new donors but may enhance the recombination frequency since cells killed by them may continue to act as chromosome donors. The effect is not shown either by uvr mutants (unable to excise thymine dimers) or by rec mutants (unable to mediate recombination) which carry an F-prime factor. A possible mechanism is suggested whereby the excision of single-stranded fragments of the bacterial chromosome, during the repair of U.V. damage, facilitates pairing with homologous regions of the complementary sex factor strand. A recombination event, mediated by breakage and covalent bonding, then joins a free end of the excised DNA strand to the paired sex factor strand. In this way, recombination connects sex factor and chromosome by only a single strand instead of by the two strands which normally leads to insertion and the formation of an Hfr chromosome. It is postulated that such a structure can be transferred at conjugation, but is incapable of more than one cycle of replication.

Chromosome Transfer in Proteus Mirabilis Mediated by a Hybrid Plasmid

“…The latter authors as well as Cooke & suggested that this factor alternated frequently between integration near the trp region and the autonomous state. Moody & Hayes (1972) also favoured some mode of RI-determined interaction with the bacterial chromosome (see also Evenchik, Stacey & Hayes, 1969) and maintained that the efficient transfer of the trp region could hardly be explained on the basis of spontaneous fragmentation and passive transfer with the sex factor only providing effective contact, as has been suggested for factor ColI (Clowes & Moody, 1966; see also Edwards Clowes, 1972). Participation of P-lacR1drd19 in the process of chromosome transfer was possibly indicated by results given in Table 6.…”

Linkage Mapping in Rhizobium leguminosarum by means of R Plasmid-mediated Recombination

“…Chromosome mobilization by F and a number of R plasmids in E. coli can arise by integration of the plasmids into the donor chromosome to form Hfr-type donors (Moody & Runge, 1972) or by some other form of interaction not requiring stable integration (Curtiss & Renshaw, 1969;Evenchik, Stacey & Hayes, 1969;Moody & Hayes, 1972). In Hfr x F-crosses, recombinants are normally F-except when the whole chromosome is transferred.…”

Properties of IncP-2 plasmids of Pseudomonas spp

“…Media and mating conditions. Nitrate nutrient broth for growing and mating strains and media for propagating bacteriophages have been described previously (16) 10. In crosses with prototrophic donors, rifampin was used for counterselection, whereas selection against auxotrophic donors was done by omission of the required supplement.…”