Involvement of DNA-dependent RNA polymerase in a recA-independent pathway of genetic recombination in Escheria coli.

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Abstract
Recombinant DNA molecules of phage .lambda. formed in E. coli in the presence of chloramphenicol and/or rifampin can be assayed by their biological activity. recA- cells formed recombinant .lambda. phage DNA in the presence of chloramphenicol. The relatively high recA-independent recombination observed in this system contrasts with the relatively low recA-independent recombination when recombinant phage particles rather than recombinant DNA are titrated. Formation of the recombinant DNA was suppressed by the addition of rifampin. The introduction of the rifr mutation into host bacteria made their recombination activity rifampin-resistant. DNA-dependent RNA polymerase (EC 2.7.7.6) is apparently involved in this recA-independent pathway of recombination, which is named the Rpo pathway. This is distinct from Red, Int, RecBC, RecE or Der pathways of recombination. Crossover was much more frequent in the N-pL-cI and cI-PR-O regions than in the A-D and O-S regions. The crossover seems to occur in the regions that are transcribed actively. Some local change of DNA structure caused by transcription might be required for the Rpo pathway of recombination.