Abstract
Conjugation is the process by which bacteria exchange genetic materials in a unidirectional manner from a donor cell to a recipient cell. The discovery of conjugation signalled the dawn of genetics and molecular biology. In Gram‐negative bacteria, the process of conjugation is mediated by a large membrane‐embedded machinery termed “conjugative type IV secretion (T4S) system”, a large injection nanomachine, which together with a DNA‐processing machinery termed “the relaxosome” and a large extracellular tube termed “pilus” orchestrates directional DNA transfer. Here, the focus is on past and latest research in the field of conjugation and T4S systems in Gram‐negative bacteria, with an emphasis on the various questions and debates that permeate the field from a mechanistic perspective.
Highlights
Bacterial conjugation is the process by which DNA is transferred unidirectionally from a donor cell to a recipient cell
Its discovery signalled the dawn of molecular biology once it was demonstrated that the transfer of genetic information was unidirectional and that the entire genome of Escherichia coli could be passed from one cell to another starting at a defined site [2]
Landmark discoveries followed: the mapping of the E. coli genome or the discovery of gene structure and regulation
Summary
Bacterial conjugation is the process by which DNA is transferred unidirectionally from a donor cell to a recipient cell. MOBF relaxases include TraI encoded by the F-family plasmids (F, R1 and pED208 for example) and TrwC encoded by the R388 plasmid Both include a helicase domain at their C-terminus but Ffamily plasmid TraI proteins have a more extensive domain structure with an N-terminal trans-esterase domain (residues 1–306) that catalyses the nicking and covalent attachment of the T-strand to the relaxase [28], a vestigial helicase domain (residues 315–828) that operates as a ssDNA-binding domain [29], an active helicase domain (residues 864–1,461) that unwinds DNA in the 50-to-30 direction, and a C-terminal domain, the function of which is still unclear but might be used as a recruitment platform for relaxosome components [30,31] (residue numbers here are for the R1 plasmid TraI; Fig 2B, upper panel). Ilangovan et al [41] have shown that full-length Ffamily TraI binds the ssDNA 50 of nic in an open conformation being susceptible to rapid proteolysis degradation, but binds ssDNA 30 of
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