To be or not to be: regulation of restriction-modification systems and other toxin-antitoxin systems.
One of the simplest classes of genes involved in programmed death is that containing the toxin-antitoxin (TA) systems of prokaryotes. These systems are composed of an intracellular toxin and an antitoxin that neutralizes its effect. These systems, now classified into five types, were initially discovered because some of them allow the stable maintenance of mobile genetic elements in a microbial population through postsegregational killing or the death of cells that have lost these systems. Here, we demonstrate parallels between some TA systems and restriction-modification systems (RM systems). RM systems are composed of a restriction enzyme (toxin) and a modification enzyme (antitoxin) and limit the genetic flux between lineages with different epigenetic identities, as defined by sequence-specific DNA methylation. The similarities between these systems include their postsegregational killing and their effects on global gene expression. Both require the finely regulated expression of a toxin and antitoxin. The antitoxin (modification enzyme) or linked protein may act as a transcriptional regulator. A regulatory antisense RNA recently identified in an RM system can be compared with those RNAs in TA systems. This review is intended to generalize the concept of TA systems in studies of stress responses, programmed death, genetic conflict and epigenetics.
Department of Microbiology, University of Gdansk, Wita Stwosza 59, Gdansk, 80-308, Poland, Department of Medical Genome Sciences, Graduate School of Frontier Sciences, University of Tokyo, Tokyo 108-8639, Japan and Institute of Medical Science, University of Tokyo, Tokyo 108-8639, Japan.
Iwona
I
Mruk
Ichizo
I
Kobayashi
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D015280:DNA Restriction-Modification Enzymes / Q000145:classification / Q000378:metabolism*; D005786:Gene Expression Regulation; D016372:RNA, Antisense / Q000378:metabolism
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D015280:DNA Restriction-Modification Enzymes; D016372:RNA, Antisense