Differential Requirements of Two recA Mutants for Constitutive SOS Expression in Escherichia coli K-12

Background Repairing DNA damage begins with its detection and is often followed by elicitation of a cellular response. In E. coli, RecA polymerizes on ssDNA produced after DNA damage and induces the SOS Response. The RecA-DNA filament is an allosteric effector of LexA auto-proteolysis. LexA is the repressor of the SOS Response. Not all RecA-DNA filaments, however, lead to an SOS Response. Certain recA mutants express the SOS Response (recAC) in the absence of external DNA damage in log phase cells. Methodology/Principal Findings Genetic analysis of two recAC mutants was used to determine the mechanism of constitutive SOS (SOSC) expression in a population of log phase cells using fluorescence of single cells carrying an SOS reporter system (sulAp-gfp). SOSC expression in recA4142 mutants was dependent on its initial level of transcription, recBCD, recFOR, recX, dinI, xthA and the type of medium in which the cells were grown. SOSC expression in recA730 mutants was affected by none of the mutations or conditions tested above. Conclusions/Significance It is concluded that not all recAC alleles cause SOSC expression by the same mechanism. It is hypothesized that RecA4142 is loaded on to a double-strand end of DNA and that the RecA filament is stabilized by the presence of DinI and destabilized by RecX. RecFOR regulate the activity of RecX to destabilize the RecA filament. RecA730 causes SOSC expression by binding to ssDNA in a mechanism yet to be determined

Vesicouterine fistula twenty years following brachytherapy for cervical cancer

This report concerns an extremely rare type of fistula, a vesicouterine fistula. in a 59-year-old female occurring twenty years following brachytherapy for cervical cancer. The patient presented with a history of recurrent urinary tract infections, sensation of incompletely emptying the bladder, nocturia and constant leakage of urine for several months. Cystoscopy revealed a fistulous opening and an exophytic lesion on the posterior bladder wall. Contrast computerized tomography demonstrated a fistulous tract between the posterior bladder wall and the anterior aspect of the uterine cavity. She underwent a hysterectomy, excision of the bladder fistula and interposition of a vascularized rectus muscle graft. Histology of the cervix and bladder only revealed inflammatory changes with no evidence of malignancy. The diagnosis and investigation of this extremely rare condition are discussed, and the management strategies outlined