PROTEIN-NUCLEOSIDE CONTACTS IN THE INTERACTION BETWEEN THE REPLICATION TERMINATOR PROTEIN OF BACILLUS-SUBTILIS AND THE DNA TERMINATOR

The interaction between the DNA replication terminator, IRI, of Bacill us subtilis and its cognate replication terminator protein (RTP) has b een examined by the technique of missing nucleoside interference (MNI) . IRI contains two adjacent binding sites (A and B) for RTP dimers. Th e B site is proximal to the replication fork arrest site. The present results have shown that nucleoside contacts with RTP in the two sites are very different. There are more extensive contacts of nucleosides i n both strands of the B site with RTP compared with the A site. The da ta also strongly suggest that filling by RTP of the B site occurs firs t and is needed for subsequent co-operative filling of an overlapping A site. The A site alone binds RTP poorly. The findings are consistent with interaction occurring between RTP dimers bound to adjacent sites of IRI, which would explain why RTP bound to the B site alone cannot cause replication fork arrest.