Autonomous plasmid-like replication of a conjugative transposon.
Integrative and conjugative elements (ICEs), a.k.a. conjugative transposons, are mobile genetic elements involved in many biological processes, including pathogenesis, symbiosis and the spread of antibiotic resistance. Unlike conjugative plasmids that are extra-chromosomal and replicate autonomously, ICEs are integrated in the chromosome and replicate passively during chromosomal replication. It is generally thought that ICEs do not replicate autonomously. We found that when induced, Bacillus subtilis ICEBs1 undergoes autonomous plasmid-like replication. Replication was unidirectional, initiated from the ICEBs1 origin of transfer, oriT, and required the ICEBs1-encoded relaxase NicK. Replication also required several host proteins needed for chromosomal replication, but did not require the replicative helicase DnaC or the helicase loader protein DnaB. Rather, replication of ICEBs1 required the helicase PcrA that is required for rolling circle replication of many plasmids. Transfer of ICEBs1 from the donor required PcrA, but did not require replication, indicating that PcrA, and not DNA replication, facilitates unwinding of ICEBs1 DNA for horizontal transfer. Although not needed for horizontal transfer, replication of ICEBs1 was needed for stability of the element. We propose that autonomous plasmid-like replication is a common property of ICEs and contributes to the stability and maintenance of these mobile genetic elements in bacterial populations.
Lee
Catherine A
CA
Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Babic
Ana
A
Grossman
Alan D
AD
D001412:Bacillus subtilis / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development / Q000472:pathogenicity; D001426:Bacterial Proteins / Q000235:genetics; D002876:Chromosomes, Bacterial / Q000235:genetics; D003227:Conjugation, Genetic; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics; D053488:DnaB Helicases / Q000235:genetics / Q000378:metabolism; D018014:Gene Transfer Techniques; D020287:In Situ Nick-End Labeling / Q000379:methods; D034982:Integration Host Factors / Q000235:genetics*; D009713:Nucleotidyltransferases / Q000235:genetics; D010957:Plasmids / Q000235:genetics*; D018741:Replication Origin / Q000235:genetics
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D034982:Integration Host Factors; C040220:DNA polymerase C; D009713:Nucleotidyltransferases; D004259:DNA-Directed DNA Polymerase; C083980:dnaN protein, Bacteria; D004265:DNA Helicases; D053488:DnaB Helicases