Controlled initiation of chromosomal replication in Escherichia coli requires functional Hda protein.

Regulatory inactivation of DnaA helps ensure that the Escherichia coli chromosome is replicated only once per cell cycle, through accelerated hydrolysis of active replication initiator ATP-DnaA to inactive ADP-DnaA. Analysis of deltahda strains revealed that the regulatory inactivation of DnaA component Hda is necessary for maintaining controlled initiation but not for cell growth or viability.

Identification of a novel membrane-associated gene product that suppresses toxicity of a TrfA peptide from plasmid RK2 and its relationship to the DnaA host initiation protein.

The toxicity of a peptide derived from the amino-terminal portion of 33-kDa TrfA, one of the initiation proteins encoded by the broad-host-range plasmid RK2, was suppressed by a host protein related to DnaA, the initiation protein of Escherichia coli. The newly identified 28.4-kDa protein, termed a DnaA paralog (Dp) because it is similar to a region of DnaA but likely has a different function in initiation of plasmid RK2 replication, interacts physically with the 33-kDa TrfA initiation protein, including the initiation-active monomeric form. The Dp has a cellular distribution similar to that of the 33-kDa TrfA initiation protein, being found primarily in the inner membrane fraction, with lesser amounts detected in the outer membrane fraction and almost none in the soluble fraction of E. coli. Maintenance and inner membrane-associated replication of plasmid RK2 were enhanced in a Dp knockout strain and inhibited in strains containing extra copies of the Dp gene or in membrane extracts to which a tagged form of Dp was added. Recently, the Dp was independently shown to help prevent overinitiation in E. coli and was termed Hda (S. Kato and T. Katayama, EMBO J. 20:4253-4262, 2001).

Highly sensitive chemiluminescence immunoassay for benzo[a]pyrene-DNA adducts: validation by comparison with other methods, and use in human biomonitoring.

A chemiluminescence immunoassay (CIA) utilizing antiserum elicited against DNA modified with (+/-)-7beta, 8alpha-dihydroxy-9alpha,10alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]- pyrene (BPDE) has been developed and validated to study the formation of polycyclic aromatic hydrocarbon (PAH)-DNA adducts in human tissues. Advantages include a low limit of detection for 10b-(deoxyguanosin-N(2)-yl)-7beta,8alpha,9alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG, approximately 1.5 adducts/10(9) nucleotides using 20 micro g DNA) and a high signal-to-noise ratio (> or =100). The CIA BPDE-DNA standard curve gave 50% inhibition at 0.60 +/- 0.08 fmol BPdG (mean +/- SE, n = 30), which was a 10-fold increase in sensitivity compared with the dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA). Calf thymus DNA modified with [1,3-(3)H]BPDE was assayed by radiolabeling, (32)P-postlabeling, DELFIA and CIA, and all assays gave similar values. Liver DNAs from mice exposed to 0.5 and 1.0 mg [7,8-(3)H]benzo[a]pyrene (BP) were assayed by the same four assays and a dose-response was obtained with all assays. The BPDE-DNA CIA was further validated in MCL-5 cells exposed to 4 micro M BP for 24 h, where nuclear and mitochondrial DNA adduct levels were associated with an increase in DNA tail length measured by the Comet assay. Human peripheral blood cell (buffy coat) DNA samples (n = 43) obtained from 25 individuals who were either colorectal adenocarcinoma patients or controls were assayed by BPDE-DNA CIA. Three samples (7%) were non-detectable, and the remaining 40 samples had values between 0.71 and 2.21 PAH-DNA adducts/10(8) nucleotides. The intra-assay coefficient of variation (CV), for four wells on the same microtiter plate, was 1.85%. Sufficient DNA for two assays, on separate plates, was available for 38 of the 43 samples, and the PAH-DNA adduct values obtained were highly correlated (r(2) = 0.95). Coded duplicate DNA samples from 15 individuals were assayed four times gave an inter-assay CV of 13.8%.