Immunoglobulin V-region somatic hypermutation and C-region class-switch recombination are initiated by activation-induced cytidine deaminase (AID) in B-cells. AID-induced DNA damage at the immunoglobulin S-region is known to be repaired by non-homologous end-joining, but repair mechanisms at the V-region remain to be elucidated. In Saccharomyces cerevisiae , DNA homologous recombination is regulated by the expression of Sac3, involved in actin assembly, cell cycle transition and mRNA metabolism. Here, we demonstrate that the Sac3-homologue GANP suppresses DNA recombination in a direct-repeat β β β β -galactosidase gene construct in mammalian cells. Homozygous ganp gene knockout is embryonic lethal in mice. Embryonic fibroblasts immortalized from hetero-deficient ganp +/-mice showed more DNA recombination than wild-type. In contrast, over-expression of GANP suppressed either spontaneous DNA recombination or that caused by the introduction of aid cDNA into NIH3T3 cells (susceptible to I-sce I restriction enzyme cleavage but not to RAG-mediated immunoglobulin gene recombination). GANP suppresses the DNA recombination not only on the extrachromosomal DNA construct but also on the integrated DNA. The Sac3-homology portion is necessary for the suppressive activity, but the truncated carboxyl terminal MCM3-binding/acetylating region adversely augmented DNA recombination, acting as a dominant negative form. Expression of full-length GANP is critical for suppression of DNA hyper-recombination in mammalian cells. IntroductionB-cells produced in the bone marrow undergo random rearrangements of immunoglobulin ( Ig ) gene segments such as V H -D H -J H and V L -J L to generate unique antigen (Ag) receptors. Naïve B-cells recruited into peripheral lymphoid organs encounter exogenous Ags and start to proliferate and differentiate with the help of Th cells in the lymphoid follicles in response to T-cell-dependent Ag. The Ag-driven B-cells undergo Ig gene V-region somatic hypermutation and class-switch recombination initiated by activation-induced cytidine deaminase (AID), generating DNA cleavages during transcription or DNA replication in germinal centers (GCs) (Honjo et al . 2002). DNA double-strand breaks (DSBs) occur in both Ig Vregions and S-regions , which are considered to be repaired by the different DNA repair mechanisms. In contrast to 1206the S-region, where DNA repair is undertaken by a nonhomologous end-joining repair (NHEJR) mechanism utilizing Ku70/Ku80, DNA-PKcs, XRCC4 and DNA ligase IV, DSB repair mechanisms at the V-region genes remained undetermined (Casellas et al . 1998;Manis et al . 1998;Meek et al . 2004;Rooney et al . 2004). DNA repair in many cells depends on homologous recombination (HR) creating single-strand DNA to anneal with the undamaged complementary strand of the paired allele during DNA replication (West 2003). HR rescues the DNA with various DNA polymerases by reading the complementary strand from the undamaged allele.In Saccharomyces cerevisiae, an inhibitor of actin assembly, Sac3, is critic...

DNA-PK was inactivated by heat treatment at 44 degrees C. Ku70/Ku80, but not Ku70 alone, could restore heat-inactivated DNA-PK.

Saccharomyces Sac3 required for actin assembly was shown to be involved in DNA replication. Here, we studied the function of a mammalian homologue SHD1 in cell cycle progression. SHD1 is localized on centrosomes at interphase and at spindle poles and mitotic spindles, similar to alpha-tubulin, at M phase. RNA interference suppression of endogenous shd1 caused defects in centrosome duplication and spindle formation displaying cells with a single apparent centrosome and down-regulated Mad2 expression, generating increased micronuclei. Conversely, increased expression of SHD1 by DNA transfection with shd1-green fluorescent protein (gfp) vector for a fusion protein of SHD1 and GFP caused abnormalities in centrosome duplication displaying cells with multiple centrosomes and deregulated spindle assembly with up-regulated Mad2 expression until anaphase, generating polyploidy cells. These results demonstrated that shd1 is involved in cell cycle progression, in particular centrosome duplication and a spindle assembly checkpoint function.

Nishiyama district in Nagasaki is located approximately 3000 m east of the hypocenter of the atomic bomb that was dropped on 9 August 1945. This district is also known as an area where there was a concentrated radioactive fallout with the black rain that was carried by a westerly wind. The Nagasaki atomic bomb was a Pu bomb, and the fallout must have included 239Pu without fission in addition to fission products. The presence of 239Pu in Nishiyama district has been confirmed previously. In this study, the distribution of 239 + 240Pu concentration in the uncultivated soil and the transfer factor of 239 + 240Pu to agricultural products in Nishiyama district were examined. The concentration of 239 + 240Pu in the uncultivated soil was 20 Bq kg-1, which was approximately eight times as high as that in the control districts. The transfer factor of 239 + 240Pu to agricultural products was 10(-4) - 10(-3), which was 1/100-1/200 of that of 137Cs.

To understand the current situation of internal radiation exposure in the population around the Chernobyl Nuclear Power Plant (CNPP), we examined the 137Cs body burden in six residents of Belarus, Ukraine and Russia in 2002 and 2004 using the whole-body counter (WBC) at Nagasaki University (Japan). The data were compared with those of our previous study performed in 1993-1994 using the same method. In 2002 and 2004, peaks of 137Cs were detected in two residents from Gomel, which was heavily contaminated by the CNPP accident, one from Minsk (Belarus) and one from Kiev (Ukraine), but another resident from Minsk showed no 137Cs peaks. The results of the present study suggests that residents around the CNPP are still exposed to chronic 137Cs internal irradiation, probably due to the daily consumption of contaminated domestic foods, but the risk of any disease by the irradiation is quite low. Long-term follow-up of WBC around the CNPP is useful and may contribute to radiation safety regulation together with a reduction of unnecessary radiophobia for the residents.