Deletions of recBCD or recD influence genetic transformation differently and are lethal together with a recJ deletion in Acinetobacter baylyi.
In prokaryotes, homologous recombination is essential for the repair of genomic DNA damage and for the integration of DNA taken up during horizontal gene transfer. In Escherichia coli, the exonucleases RecJ (specific for 5' single-stranded DNA) and RecBCD (degrades duplex DNA) play important roles in recombination and recombinational double-strand break (DSB) repair by the RecF and RecBCD pathways, respectively. The cloned recJ of Acinetobacter baylyi partially complemented an E. coli recJ mutant, suggesting functional similarity of the enzymes. A DeltarecJ mutant of A. baylyi was only slightly altered in transformability and was not affected in UV survival. In contrast, a DeltarecBCD mutant was UV-sensitive, and had a low viability and altered transformation. Compared to wild-type, transformation with large chromosomal DNA fragments was decreased about 5-fold, while transformation with 1.5 kbp DNA fragments was increased 3.3- to 7-fold. A DeltarecD mutation did not affect transformation, viability or UV resistance. However, double mutants recJ recBCD and recJ recD were non-viable, suggesting that the RecJ DNase or the RecBCD DNase (presumably absent in recD) becomes essential for the recombinational repair of spontaneously inactivated replication forks if the other DNase is absent. A model of recombination during genetic transformation is discussed in which the two ends of the single-stranded donor DNA present in the cytoplasm frequently integrate separately and often with a time difference. If replication runs through that genomic region before both ends of the donor DNA are ligated to recipient DNA, a double-strand break (DSB) is formed. In these cases, transformation becomes dependent on DSB repair.
Kickstein
Eva
E
Genetics, Department of Biology and Environmental Sciences, Carl von Ossietzky University Oldenburg, D-26111 Oldenburg, Germany.
Harms
Klaus
K
Genetics, Department of Biology and Environmental Sciences, Carl von Ossietzky University Oldenburg, D-26111 Oldenburg, Germany.
Wackernagel
Wilfried
W
Genetics, Department of Biology and Environmental Sciences, Carl von Ossietzky University Oldenburg, D-26111 Oldenburg, Germany.
D000150:Acinetobacter / Q000201:enzymology / Q000235:genetics* / Q000528:radiation effects*; D001426:Bacterial Proteins / Q000378:metabolism; D004260:DNA Repair; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D043211:Exodeoxyribonuclease V / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D005090:Exodeoxyribonucleases / Q000172:deficiency* / Q000378:metabolism; D017353:Gene Deletion; D005798:Genes, Bacterial; D009692:Nucleic Acid Heteroduplexes / Q000235:genetics; D011995:Recombination, Genetic; D014170:Transformation, Genetic; D014466:Ultraviolet Rays
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D009692:Nucleic Acid Heteroduplexes; D005090:Exodeoxyribonucleases; C070765:recJ protein, Bacteria; D043211:Exodeoxyribonuclease V