Figure 8.

Scheme of the proposed regulation of pIP501 by TraN and the relaxase TraA. (A) Regulation of tra-operon expression by TraN and TraA. (1) The expression of Tra-proteins from the tra-operon is initiated and mRNA is produced from the P_tra and the P_traNO promoters. (2) The relaxase TraA binds to its binding site at the P_tra promoter and controls the level of tra-operon transcription, while the P_traNO promoter remains active. Simultaneously, Tra-proteins are produced and the mating pair formation (MPF) complex assembles at the bacterial membrane. (3) TraN binding to its binding sites upstream of the P_tra and the P_traNO promoters leads to repression of transcription. (B) Initiation of conjugative transfer by the relaxase TraA. Responding to yet unknown signals, conjugative processes are initiated by the relaxase TraA introducing a single-strand (ss) cut at the origin of transfer (oriT). TraN is released from its binding site at the P_trapromoter and replication takes place in the donor, while the ss-DNA is transferred to the recipient.