Tandem repeat deletion in the alpha C protein of group B streptococcus is recA independent.
Group B streptococci (GBS) contain a family of protective surface proteins characterized by variable numbers of repeating units within the proteins. The prototype alpha C protein of GBS from the type Ia/C strain A909 contains a series of nine identical 246-bp tandem repeat units. We have previously shown that deletions in the tandem repeat region of the alpha C protein affect both the immunogenicity and protective efficacy of the protein in animal models, and these deletions may serve as a virulence mechanism in GBS. The molecular mechanism of tandem repeat deletion is unknown. To determine whether RecA-mediated homologous recombination is involved in this process, we identified, cloned, and sequenced the recA gene homologue from GBS. A strain of GBS with recA deleted, A909DeltarecA, was constructed by insertional inactivation in the recA locus. A909DeltarecA demonstrated significant sensitivity to UV light, and the 50% lethal dose of the mutant strain in a mouse intraperitoneal model of sepsis was 20-fold higher than that of the parent strain. The spontaneous rate of tandem repeat deletion in the alpha C protein in vitro, as well as in our mouse model of immune infection, was studied using A909DeltarecA. We report that tandem repeat deletion in the alpha C protein does occur in the absence of a functional recA gene both in vitro and in vivo, indicating that tandem repeat deletion in GBS occurs by a recA-independent recombinatorial pathway.
Puopolo
K M
KM
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, USA. kpuopolo@rics.bwh.harvard.edu
Hollingshead
S K
SK
Carey
V J
VJ
Madoff
L C
LC
D000818:Animals; D000954:Antigens, Surface / Q000235:genetics* / Q000276:immunology; D001426:Bacterial Proteins / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D015153:Blotting, Western; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D003627:Data Interpretation, Statistical; D004195:Disease Models, Animal; D005798:Genes, Bacterial; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods; D011938:Rec A Recombinases / Q000235:genetics*; D018805:Sepsis / Q000382:microbiology; D017384:Sequence Deletion; D013154:Spleen / Q000382:microbiology; D013290:Streptococcal Infections / Q000382:microbiology*; D013292:Streptococcus agalactiae / Q000235:genetics* / Q000276:immunology / Q000302:isolation & purification; D020080:Tandem Repeat Sequences
D000954:Antigens, Surface; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C077961:alpha C protein, group B streptococci; D011938:Rec A Recombinases