Abstract
Bacterial conjugation is the main horizontal gene transfer route responsible for the spread of antibiotic resistance, virulence and toxin genes. During conjugation, DNA is transferred from a donor to a recipient cell via a sophisticated channel connecting the two cells. Conjugation not only affects many different aspects of the plasmid and the host, ranging from the properties of the membrane and the cell surface of the donor, to other developmental processes such as competence, it probably also poses a burden on the donor cell due to the expression of the large number of genes involved in the conjugation process. Therefore, expression of the conjugation genes must be strictly controlled. Over the past decade, the regulation of the conjugation genes present on the conjugative Bacillus subtilis plasmid pLS20 has been studied using a variety of methods including genetic, biochemical, biophysical and structural approaches. This review focuses on the interplay between RcopLS20, RappLS20 and Phr*pLS20, the proteins that control the activity of the main conjugation promoter Pc located upstream of the conjugation operon. Proper expression of the conjugation genes requires the following two fundamental elements. First, conjugation is repressed by default and an intercellular quorum-signaling system is used to sense conditions favorable for conjugation. Second, different layers of regulation act together to repress the Pc promoter in a strict manner but allowing rapid activation. During conjugation, ssDNA is exported from the cell by a membrane-embedded DNA translocation machine. Another membrane-embedded DNA translocation machine imports ssDNA in competent cells. Evidences are reviewed indicating that conjugation and competence are probably mutually exclusive processes. Some of the questions that remain unanswered are discussed.
Highlights
Horizontal Gene Transfer (HGT) refers to the process by which a DNA element/region is transferred from one cell to another
In this review we describe the advances that have been made in recent years in understanding how expression of the pLS20 conjugation genes is regulated, and identify the similarities and differences with two other conjugative systems of Gram+ origin
The most important gaps of knowledge concern structural insights in 1) how repressor molecules generate DNA looping, 2) how the antirepressor interacts with the repressor, and 3) if and how genes involved in different steps of the conjugation process–all located in a single large operon-are differentially expressed
Summary
Horizontal Gene Transfer (HGT) refers to the process by which a DNA element/region is transferred from one cell to another. A DNA element is transferred from a donor cell to a recipient cell; it requires direct contact between the two cells. In stage 2) the conjugation element is processed to generate the DNA that is transferred to the recipient cell, which in most cases is single-stranded DNA (ssDNA). Very little was known about conjugation systems present on B. subtilis plasmids, as a host B. subtilis is one of the best studied G+ bacteria (Sonenshein et al, 1993; sonenshein et al, 2001). The most important gaps of knowledge concern structural insights in 1) how repressor molecules generate DNA looping, 2) how the antirepressor interacts with the repressor, and 3) if and how genes involved in different steps of the conjugation process–all located in a single large operon-are differentially expressed. Protein p27c, is a putative Xre-type transcriptional regulator predicted to contain a typical DNA binding Helix-Turn-Helix (HTH) domain near its EVIDENCE THAT pLS20 CONJUGATION IS
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
