A R Lehmann

..Many studies have been carried out on the properties of the other polymerases in vitro, but there is as yet very little evidence for their specific roles in vivo...

..Emerging evidence suggests that the polymerase switch from replicative to translesion polymerases might be mediated by post-translational modifications...

..Skin tumours in XP patients have mutations characteristic of UV-induction in the ras, p53 and ptch genes, showing that sunlight-induced mutations in these genes are important in carcinogenesis in XP patients...

..The Smc5-6 complex is involved in a variety of DNA repair and damage response pathways by as yet unknown mechanisms, but is also associated with repair by homologous recombination...

..These polymerases are located in replication factories during DNA replication and the polymerase sliding clamp PCNA plays an important role in mediating switching between different polymerases...

..The clamps are dimeric in bacteria and trimeric in eukaryotes and archaea, raising the question of whether more than one polymerase can interact with the clamp simultaneously. Recently published data suggest that this is indeed the case...

..Apart from anticipated helicase domains the structures reveal a 4FeS cluster and novel "Arch" domain. The structures help our understanding of genotype-phenotype relationships in the XPD gene...

..When the fork is blocked PCNA gets ubiquitinated. This increases its affinity for the TLS polymerases, which all have novel ubiquitin-binding motifs, thereby facilitating their engagement at the stalled fork to effect TLS...

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..In the absence of neurological problems and with lifetime protection against sunlight, the prognosis is good. In patients with neurological problems, these are progressive, leading to disabilities and a shortened lifespan...

..All the Y-family polymerases have ubiquitin binding sites that increase their binding affinity for ubiquitinated PCNA at the sites of stalled forks...

..In vitro studies implicated the replicative polymerases in repair synthesis, but recent in vivo data have shown that several DNA polymerases and ligases are involved in these steps in human cells...

..The Y-family polymerases themselves can be ubiquitinated and, in the case of DNA polymerase η, this results in the polymerase being excluded from chromatin...

..These studies have also defined an element of the radiation sensitivity caused by loss of Rad17 function which is not associated with the radiation-induced G2 arrest defect seen in the rad17.d null mutant cells...

..Analysis of radiation sensitivity though the cell cycle indicates that, unlike most other rad mutants, rad8 is most sensitive to irradiation during the G1/S period...

..Both hSMC5 and hSMC6 proteins are expressed at extremely high levels in the testis and associate with the sex chromosomes in the late stages of meiotic prophase, suggesting a possible role for these proteins in meiosis...

..This second repair pathway involves the products of the rhp51 gene (the homolog of the RAD51 gene of S. cerevisiae) and the rad2 gene...

..Our findings highlight the complexities of genotype-phenotype relationships in the XPD gene...

..We have identified an important mutation (S1045A) near the C-terminus of Rad18 that separates its repair and essential roles. Potential models for the role of the Rad18-Spr18 complex during DNA repair are discussed...

..A-T cells therefore appear to harbour dual checkpoint/repair defects. Here, we review the evidence supporting this contention and consider its implications for an analysis of the A-T phenotype...

..The patients are all compound heterozygotes and the locations of the mutations enable us to suggest relationships between different domains in the gene and its roles in excision repair and transcription...

..Codon usage suggests that the gene is very poorly expressed, and this was confirmed by RNA studies. Gene disruption showed that the rad4 gene was essential for the mitotic growth of S. pombe...

..Our results confirm the extreme ionizing radiation hypersensitivity of ataxia-telangiectasia; they are also consistent with a tendency for slight hypersensitivity in CS, but not (necessarily) in combined XP/CS...

..These findings define new functional domains involved in excision-repair, as well as identifying a conserved family of genes related to RAD2...

..If we eliminate the null mutations, the remaining mutagenic pattern is consistent with the site of the mutation determining the phenotype...

..The involvement of repair proteins in other processes also poses interesting evolutionary questions...

..Neither the site nor the nature of the mutation correlated with the severity of the clinical features. Severe truncations were found in different patients with either classical or early-onset forms of the disease...

..It is important to resolve how widespread ionizing radiation sensitivity is amongst XP patients...

..Our findings provide an attractive mechanism by which monoubiquitination of PCNA might mediate the polymerase switch...

..CONCLUSIONS: The small amount of normally spliced mRNA detected may be sufficient to explain the relatively mild clinical features in our patient...

..SA strain. Since nse2.SA cells are sensitive to DNA-damaging agents and to exposure to hydroxyurea, this implicates the Nse2-dependent sumoylation activity in DNA damage responses but not in the essential function of the Smc5-6 complex...

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..The defect, however, may confer a predisposition to leukaemia...

..Our results provide strong evidence that poleta targets poliota to the replication machinery, where it may play a general role in maintaining genome integrity as well as participating in translesion DNA synthesis...

..In initial steps to understand the architecture of the complex, we identified two subcomplexes containing Rad18-Spr18-Nse2 and Nse1-Nse3-Rad62. The subcomplexes are probably bridged by a weaker interaction between Nse2 and Nse3...

..There is a wide variability in clinical features among patients, which is not obviously related to the site or type of mutation...

..Prevention of PCNA ubiquitination sensitises the cells to killing by both UV and HU...

..Our results provide strong evidence that poleta targets poliota to the replication machinery, where it may play a general role in maintaining genome integrity as well as participating in translesion DNA synthesis...

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..This represents a strong candidate for the inactivating mutation in DNA-PKcs in the scid mouse...

..pombe. Replacement of the pcn1 locus with PCNA N-terminally tagged with different epitopes resulted in lethality, probably because the tagged proteins were expressed at substantially reduced levels...

..Several recent papers suggest that they might have other roles as well in gene conversion, in nucleotide excision repair (NER), and in DNA replication under stressed conditions...

..We show that PCNA modification and cell cycle checkpoints represent two independent signals in response to DNA damage. Finally, we unexpectedly find that PCNA is ubiquitinated in response to DNA damage when cells are arrested in G2...

..We further show that Nse3, as well as Nse5 and Nse6, also bridge the heads of Smc5 and -6. The Nse1-Nse3-Nse4 and Nse5-Nse6 subcomplexes bind to the Smc5-Smc6 heads domain at different sites...

..When DNA is exposed at replication forks, the polymerase residence times increase, and this is further facilitated by the ubiquitination of PCNA...

..The C-terminal 97 amino acids of pol(kappa)are sufficient for this limited localisation into nuclear foci, and include a C2HC zinc finger, bipartite nuclear localisation signal and putative PCNA binding site...

..One possibility is that spontaneous mutation may often occur in bursts when an error correction mechanism (eg., proofreading, mismatch correction) is temporarily inactive.(ABSTRACT TRUNCATED AT 250 WORDS)..

..Our results provide evidence for an unexpected role for pol kappa in mammalian NER...

..We present a model of translesion synthesis behind the replication fork to explain the persistence of ubiquitinated PCNA...

..Gene deletion experiments indicate that, like the S. cerevisiae RAD3 gene, the S. pombe rad15 gene is essential for viability, suggesting that the protein product has a role in cell proliferation and not solely in DNA repair...

..Depletion also confers sensitivity to methyl methanesulfonate. Several of the components are modified by sumoylation and ubiquitination...

..We point out some apparent differences between mechanisms in Saccharomyces cerevisiae and human cells...

..Like CS fibroblasts, XPCS and TTD fibroblasts from human and mouse showed evidence of defective repair of oxidative DNA lesions that may underlie these segmental progeroid symptoms...

..This review addresses recent advances in our understanding of DNA polymerase switching during TLS in bacteria such as E. coli and in lower and higher eukaryotes...

..Together, these data show that pol eta represents an important determinant of cellular responses to cisplatin, which could have implications for acquired or intrinsic resistance to this key chemotherapeutic agent...

..Thus, PCNA, acting as both a scaffold and a modulator of the different activities involved in replication, appears to recruit and coordinate replicative and translesion DNA synthesis polymerases to ensure genome integrity...

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..Our results indicate that Ub-binding domains of Y-family polymerases play crucial regulatory roles in TLS...

..This hREV1 nuclear localization occurs independently of the presence of hpol eta. Taken together, our data suggest a central role for hREV1 as a scaffold that recruits DNA polymerases involved in TLS...

..Despite these similarities between our two patients, their clinical features are quite different and the clinical severity correlates with other cellular responses to ultraviolet irradiation...

..Current progress in this rapidly expanding field was the subject of an EMBO workshop, Maintenance of Genomic Integrity, that took place in June 2004 in Galway, Ireland. Top..

..These results clearly show the protective role of pol eta against UV-induced lesions and the activation by UV of pol eta-independent mutagenic processes...

..1 per million for TTD. Perhaps contrary to general conceptions, compared to XP the incidence of CS appears to be somewhat higher and the incidence of TTD to be quite similar in the native West-European population...

..Mutations in TTDN1 do not affect the response to ultraviolet (UV) light or the steady state level of the repair/transcription factor IIH (TFIIH), which is central to the onset of the photosensitive form of TTD...