BACTERIOPHAGE-PHI-29 DNA-REPLICATION ARREST CAUSED BY CODIRECTIONAL COLLISIONS WITH THE TRANSCRIPTION MACHINERY

The consequences on replication of collisions between phi 29 DNA polym erase, a monomeric replicase endowed with strand displacement capacity , and the transcription machinery have been studied in vitro. Codirect ional collisions with stalled transcription ternary complexes at four different promoters in the phi 29 genome were found to block replicati on fork progression. Upon collision, the DNA polymerase remained on th e template and was able to resume elongation once the RNA polymerase w as allowed to move. Collisions with RNA polymerase molecules moving in the same direction also interfered with replication, causing a decrea se in the replication rate. These results lead to the proposal that in bacteriophage phi 29 a transcription complex physically blocks the pr ogression of a replication fork, We suggest that temporal regulation o f transcription and the low probability that the replication and trans cription processes colocalize in vivo contribute to achieving minimal interference between the two events.