Resolution of head-on collisions between the transcription machinery and bacteriophage Phi 29 DNA polymerase is dependent on RNA polymerase translocation

The outcome of collisions between Bacillus subtilis phage Phi 29 DNA polyme rase and oppositely oriented transcription complexes has been studied in vi tro. We found that the replication fork was unable to go past a transcripti on ternary complex stalled head-on. However, head-on collisions did not lea d to a deadlock, Both DNA and RNA polymerase remained bound to the template and, when the halted transcription complex was allowed to move, the replic ation machinery resumed normal elongation. These results suggested that a r eplication fork that encounters an RNA polymerase head-on whose movement is not impeded would bypass the transcription machinery. Our results for head -on collisions between concurrently moving replication and transcription co mplexes are indeed consistent with the existence of a resolving mechanism. The ability of Phi 29 DNA polymerase to resolve head-on collisions with its elf during symmetrical replication of Phi 29 DNA in vivo is likely to be re lated to its ability to pass a head-on oriented RNA polymerase.