Homologous recombination at the border: insertion-deletions and the trapping of foreign DNA in Streptococcus pneumoniae.
Integration of foreign DNA was observed in the Gram-positive human pathogen Streptococcus pneumoniae (pneumococcus) after transformation with DNA from a recombinant Escherichia coli bacteriophage lamda carrying a pneumococcal insert. Segments of lamda DNA replaced chromosomal sequences adjacent to the region homologous with the pneumococcal insert, whence the name insertion-deletion. Here we report that a pneumococcal insert was absolutely required for insertion-deletion formation, but could be as short as 153 bp; that the sizes of foreign DNA insertions (289-2,474 bp) and concomitant chromosomal deletions (45-1,485 bp) were not obviously correlated; that novel joints clustered preferentially within segments of high GC content; and that the crossovers in 29 independent novel joints were located 1 bp from the border or within short (3-10 nt long) stretches of identity (microhomology) between resident and foreign DNA. The data are consistent with a model in which the insert serving as a homologous recombination anchor favors interaction and subsequent illegitimate recombination events at microhomologies between foreign and resident sequences. The potential of homology- directed illegitimate recombination for genome evolution was illustrated by the trapping of functional heterologous genes.
Prudhomme
Marc
M
Laboratoire de Microbiologie et Génétique Moléculaire, Unité Mixte de Recherche 5100, Centre National de la Recherche Scientifique-Université Paul Sabatier, 118 Route de Narbonne, 31062 Toulouse Cedex, France.
Libante
Virginie
V
Claverys
Jean-Pierre
JP
D001426:Bacterial Proteins; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D017353:Gene Deletion; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D011995:Recombination, Genetic; D013296:Streptococcus pneumoniae / Q000235:genetics*
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C084499:HexA protein, bacteria; D011994:Recombinant Proteins; D004247:DNA