MECHANISTIC STUDIES ON THE IMPACT OF TRANSCRIPTION ON SEQUENCE-SPECIFIC TERMINATION OF DNA-REPLICATION AND VICE-VERSA

Since DNA replication and transcription often temporally and spatially overlap each other, the impact of one process on the other is of cons iderable interest. We have reported previously that transcription is i mpeded at the replication termini of Escherichia coli and Bacillus sub tilis in a polar mode and that, when transcription is allowed to invad e a replication terminus from the permissive direction, arrest of repl ication fork at the terminus is abrogated. In the present report, we h ave addressed four significant questions pertaining to the mechanism o f transcription impedance by the replication terminator proteins, Is t ranscription arrested at the replication terminus or does RNA polymera se dissociate from the DNA causing authentic transcription termination ? How does transcription cause abrogation of replication fork arrest a t the terminus? Are the points of arrest of the replication fork and t ranscription the same or are these different? Are eukaryotic RNA polym erases also arrested at prokaryotic replication termini? Our results s how that replication terminator proteins of E, coli and B. subtilis ar rest but do not terminate transcription, Passage of an RNA transcript through the replication terminus causes the dissociation of the termin ator protein from the terminus DNA, thus causing abrogation of replica tion fork arrest. DNA and RNA chain elongation are arrested at differe nt locations on the terminator sites, Finally, although bacterial repl ication terminator proteins blocked yeast RNA polymerases in a polar f ashion, a yeast transcription terminator protein (Reb1p) was unable to block T7 RNA polymerase and E, coli DnaB helicase.