Bacteria, even from different genera or species, can exchange genetic material through a process called bacterial conjugation. During this transfer, DNA molecules like plasmids (extrachromosomal circular DNA) move from one cell to another. These plasmids often carry genes that confer new capabilities, including antibiotic resistance, making conjugation a public health concern.
Conjugation requires a complex molecular machinery and precise control. A team led by Wilfried Meijer from CBM-CSIC-UAM has identified a new regulatory mechanism in the pLS20 plasmid of the bacterium Bacillus subtilis.
The study reveals that a very long RNA molecule, which encodes conjugation proteins, can adopt two distinct forms. One form allows continuous reading of DNA by RNA polymerase, while the other halts the process. This RNA acts as a molecular switch, deciding whether conjugation genes are activated.
The shape change occurs when two complementary sequences within the RNA pair up, closing the structure like a zipper. The interruption of this closure, caused by small RNA structures, acts as a stop signal. If the closure is not interrupted, the polymerase continues, generating the necessary RNA to produce conjugation proteins. Meijer has named this mechanism 'zipper-type transcriptional attenuator'.
This 'zipper' mechanism may be widespread in many bacteria, as similar RNA sequences have been found in other plasmids of the pLS20 family and in plasmids of Gram-positive bacteria. Understanding this regulation is vital for addressing the spread of antibiotic resistance.
The finding, published in Nucleic Acids Research, opens possibilities for designing strategies to interfere with bacterial DNA transfer and thus the dissemination of resistance genes. The research involved collaboration with teams from Pennsylvania State University (USA), the University of Groningen (Netherlands), and Newcastle University (UK).
