title: Retrotransposition strategies of the Lactococcus lactis Ll.LtrB group II intron are dictated by host identity and cellular environment.
abstract: Group II introns are mobile retroelements that invade their cognate intron-minus gene in a process known as retrohoming. They can also retrotranspose to ectopic sites at low frequency. Previous studies of the Lactococcus lactis intron Ll.LtrB indicated that in its native host, as in Escherichia coli, retrohoming occurs by the intron RNA reverse splicing into double-stranded DNA (dsDNA) through an endonuclease-dependent pathway. However, in retrotransposition in L. lactis, the intron inserts predominantly into single-stranded DNA (ssDNA), in an endonuclease-independent manner. This work describes the retrotransposition of the Ll.LtrB intron in E. coli, using a retrotransposition indicator gene previously employed in our L. lactis studies. Unlike in L. lactis, in E. coli, Ll.LtrB retrotransposed frequently into dsDNA, and the process was dependent on the endonuclease activity of the intron-encoded protein. Further, the endonuclease-dependent insertions preferentially occurred around the origin and terminus of chromosomal DNA replication. Insertions in E. coli can also occur through an endonuclease-independent pathway, and, as in L. lactis, such events have a more random integration pattern. Together these findings show that Ll.LtrB can retrotranspose through at least two distinct mechanisms and that the host environment influences the choice of integration pathway. Additionally, growth conditions affect the insertion pattern. We propose a model in which DNA replication, compactness of the nucleoid and chromosomal localization influence target site preference.
authors.affiliation: Molecular Genetics Program, Wadsworth Center, New York State Department of Health, Center for Medical Sciences, 150 New Scotland Avenue, Albany, NY 12201-2002, USA.
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Coros
authors.forename: Markus
authors.initials: M
authors.lastname: Landthaler
authors.forename: Carol Lyn
authors.initials: CL
authors.lastname: Piazza
authors.forename: Arthur
authors.initials: A
authors.lastname: Beauregard
authors.forename: Donna
authors.initials: D
authors.lastname: Esposito
authors.forename: Jiri
authors.initials: J
authors.lastname: Perutka
authors.forename: Alan M
authors.initials: AM
authors.lastname: Lambowitz
authors.forename: Marlene
authors.initials: M
authors.lastname: Belfort
mesh_terms: D001426:Bacterial Proteins; D004261:DNA Replication; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000235:genetics*; D004277:DNA, Single-Stranded / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D007438:Introns / Q000235:genetics*; D013294:Lactococcus lactis / Q000235:genetics*; D008954:Models, Biological; D008957:Models, Genetic; D018626:Retroelements / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D029968:Escherichia coli Proteins; C099786:LtrB protein, Lactococcus lactis; D018626:Retroelements