Typhimurium UK-1 (Luo, Kong, I-BET-762 nmr Golden and Curtiss, unpublished whole genome sequence), S. Paratyphi A (NC_006511) KU55933 order [48] and S. Typhi Ty2 (NC_004631) [49]. No paralogs of the recA, recF and recJ genes were found in the three strains. The S. Typhimurium UK-1 has RecA, RecO and RecR protein sequences identical to Typhi Ty2, and RecF and RecJ protein sequences with over 99% identity. Plasmids expressing Typhimurium recF or Typhi recF complemented the ΔrecF126 mutation in Typhi, as evidenced by the UV sensitivity profile

(Figure 4) and intraplasmid recombination of pYA4463 (Table 3). Therefore, the basis for these differences are not clear and indicates that there may be other genes or gene products involved. A more detailed analysis of this phenomenon is under investigation. Plasmid recombination frequencies were higher in our Salmonella strains than those reported in E. coli. We observed intra- and interplasmid recombination frequencies on the order of 1 × 10-3 in Rec+ Salmonella, whereas measurements made in E. coli strain AB1157 using a similar plasmid system (equivalent to our substrates pYA4590 and pYA4464 + pYA4465) revealed

a basal frequency around 10-fold lower, approximately 1 × 10-4 for both types of substrates [26]. Interestingly, the effect of a recF mutation in E. coli was to reduce the recombination frequency of intra- and interplasmid recombination approximately 30-fold, to roughly the same frequencies we observed for S. Typhimurium (Table 3). However, consistent selleck chemicals with the results in E. coli, the effects of recA, recF, and recA recF mutations were similar, indicating that the mutations are epistatic. RecF has been shown previously to play a role in recombinational repair of chromosomal DNA in response to DNA damaging agents [50], including a major role in homologous Prostatic acid phosphatase recombination between direct repeats in the chromosome of S. Typhimurium.

In our study, we did not observe any effect of recF on intrachromosomal recombination, although it did have an effect on the frequency of plasmid integration (Table 4). This discrepancy can be explained by the fact that we did not use DNA damaging agents in our study. These agents lead to single stranded stretches of DNA that represent substrates for recF (and recA). Our observation that recF did affect plasmid integration may reflect the presence of stretches of ssDNA in the plasmid, presumably due to supercoiling effects. To induce strong primary and memory immune responses, Salmonella delivery vectors should be sufficiently invasive and persistent to allow antigen expression in targeting organs, while maintaining a high degree of safety. This requires the use of mutations that attenuate the Salmonella vector without impairing its antigen delivery ability. Many attenuating mutations impair invasion and colonization ability. In our study, we confirmed a previous report that recF is not required for S.