Xeroderma pigmentosum variant (XP-V) is an inherited disorder which is associated with increased incidence of sunlight-induced skin cancers. Unlike other xeroderma pigmentosum cells (belonging to groups XP-A to XP-G), XP-V cells carry out normal nucleotide-excision repair processes but are defective in their replication of ultraviolet-damaged DNA. It has been suspected for some time that the XPV gene encodes a protein that is involved in trans-lesion DNA synthesis, but the gene product has never been isolated. Using an improved cell-free assay for trans-lesion DNA synthesis, we have recently isolated a DNA polymerase from HeLa cells that continues replication on damaged DNA by bypassing ultraviolet-induced thymine dimers in XP-V cell extracts. Here we show that this polymerase is a human homologue of the yeast Rad30 protein, recently identified as DNA polymerase eta. This polymerase and yeast Rad30 are members of a family of damage-bypass replication proteins which comprises the Escherichia coli proteins UmuC and DinB and the yeast Rev1 protein. We found that all XP-V cells examined carry mutations in their DNA polymerase eta gene. Recombinant human DNA polymerase eta corrects the inability of XP-V cell extracts to carry out DNA replication by bypassing thymine dimers on damaged DNA. Together, these results indicate that DNA polymerase eta could be the XPV gene product.

Xeroderma pigmentosum variant (XP-V) represents one of the most common forms of this cancer-prone DNA repair syndrome. Unlike classical XP cells, XP-V cells are normal in nucleotide excision repair but defective in post-replication repair. The precise molecular defect in XP-V is currently unknown, but it appears to be a protein involved in translesion synthesis. Here we established a sensitive assay system using an SV40 origin-based plasmid to detect XP-V complementation activity. Using this system, we isolated a protein from HeLa cells capable of complementing the defects in XP-V cell extracts. The protein displays novel DNA polymerase activity which replicates cyclobutane pyrimidine dimer-containing DNA templates. The XPV polymerase activity was dependent on MgCl 2 , sensitive to NEM, moderately sensitive to KCl, resistant to both aphidicolin and ddTTP, and not stimulated by PCNA. In glycerol density gradients, the activity co-sedimented with a 54 kDa polypeptide at 3.5S, indicating that the monomeric form of this polypeptide was responsible for the activity. The protein factor corrected the translesion defects of extracts from three XPV cell strains. Bypass DNA synthesis by the XP-V polymerase occurred only in the presence of dATP, indicating that it can incorporate only dATP to bypass a di-thymine lesion.

Liver cirrhosis is characterized by the hyper-accumulation Liver fibrosis/cirrhosis is characterized by hyper-accumulaof connective tissue components in the liver and is often tion of fibrous tissue components and is commonly observed accompanied by hypo-albuminemia, ascites, and esophageal in later or terminal states of chronic hepatic diseases. In ongovarices. In a prolonged stage, severe hepatic failure, or hepaing work, we found that the administration of human recombitocellular carcinoma, can occur. Chronic hepatic injuries nant hepatocyte growth factor (hrHGF) suppressed the onset caused by drugs, chemicals, alcohol abuse, or viral infections of liver fibrosis/cirrhosis in several distinct models and accelare predominant pathogenic causes for cirrhosis. Although erated the recovery from liver fibrosis/cirrhosis in rats. Rethe pathogenic mechanisms of cirrhosis are not fully underpeated administration of porcine serum for 10 weeks to rats stood, the over-production of extracellular matrices in the induced liver fibrosis without any accompanying hepatocelluliver, as well as of chronic parenchymal hepatocellular injury, lar injuries; in addition, the intravenous (i.v.) administration are likely to initiate the onset of cirrhosis. Therefore, preferof hepatocyte growth factor (HGF) to these rats suppressed ential hepatocellular replication and cytoprotection against increases in fibrous components and hydroxyproline contents hepatic injuries, as well as the stimulation of degradation in the liver, thus preventing the onset of liver fibrosis. Reand remodeling of extracellular fibrous components, seems peated administration of dimethylnitrosamine (DMN) for four to inhibit the onset or progress of hepatic fibrosis/cirrhosis. weeks induced liver cirrhosis, as characterized by the hyperSeveral lines of studies have shown that hepatocyte growth accumulation of fibrous components, infiltration of mononufactor (HGF), originally purified as a potent mitogen for rat clear leukocytes, and hepatic dysfunction. When HGF was hepatocytes, 1-3 is the long-sought hepatotrophic factor for injected daily for four weeks along with DMN-treatment, the liver regeneration. [4][5][6][7] Following the onset of various types of onset of DMN-induced hepatic fibrosis/cirrhosis was suphepatic injuries, HGF messenger RNA expression is rapidly pressed; the numbers of infiltrating mononuclear cells, fibrous tissue components, and hydroxyproline content in the liver up-regulated in the livers of experimental animals. 8,9 Serum were decreased. When HGF was injected for two weeks fol-HGF levels are elevated in patients with various hepatic dislowing four weeks of DMN-treatment, HGF accelerated the orders. 10,11 Extensive in vivo studies on the efficacy of recomrecovery from liver cirrhosis and prevented death due to he-binant HGF on hepatic regeneration revealed that HGF elicits patic dysfunction. Likewise, HGF-injection suppressed the on-a potent hepatotrophic action. HGF strongly stimulates DNA set of liver fibrosis, when liver fibrosis had be...

swallowtail butterflies belonging to the family of Papilionidae selectively utilize a limited number of plants from a single or a few families. Female butterflies lay eggs on their host only when they detect specific chemicals through their foreleg chemosensilla while drumming on the leaf surface. Here we show that the butterfly, Papilio xuthus, uses a gustatory receptor specific for synephrine to select its host in oviposition behaviour. We identify a gustatory receptor gene involved in the recognition of an oviposition stimulant, synephrine, from the P. xuthus by a combination of in silico, in vitro and in vivo approaches. The receptor, PxutGr1, responds specifically to synephrine in sf9 cells. The sensitivity of tarsal taste sensilla to synephrine and the oviposition behaviour in response to synephrine are strongly reduced after injecting double-stranded RnA of PxutGr1 into pupae. These observations indicate that the receptor PxutGr1 represents a key factor in host specialization in P. xuthus.

DNA polymerase(Pol ) is the product of the Polh gene, which is responsible for the group variant of xeroderma pigmentosum, a rare inherited recessive disease which is characterized by susceptibility to sunlightinduced skin cancer. We recently reported in a study of Polh mutant mice that Pol is involved in the somatic hypermutation of immunoglobulin genes, but the cancer predisposition of Polh ؊/؊ mice has not been examined until very recently. Another translesion synthesis polymerase, Pol , a Pol paralog encoded by the Poli gene, is naturally deficient in the 129 mouse strain, and the function of Pol is enigmatic. Here, we generated Polh Poli doubledeficient mice and compared the tumor susceptibility of them with Polh-or Poli-deficient animals under the same genetic background. While Pol deficiency does not influence the UV sensitivity of mouse fibroblasts irrespective of Polh genotype, Polh Poli double-deficient mice show slightly earlier onset of skin tumor formation. Intriguingly, histological diagnosis after chronic treatment with UV light reveals that Pol deficiency leads to the formation of mesenchymal tumors, such as sarcomas, that are not observed in Polh ؊/؊ mice. These results suggest the involvement of the Pol and Pol proteins in UV-induced skin carcinogenesis.

hHR23B was originally isolated as a component of a protein complex that specifically complements nucleotide excision repair (NER) defects of xeroderma pigmentosum group C cell extracts in vitro and was identified as one of two human homologs of the Saccharomyces cerevisiae NER gene product Rad23. Recombinant hHR23B has previously been shown to significantly stimulate the NER activity of recombinant human XPC protein (rhXPC). In this study we identify and functionally characterize the XPC-binding domain of hHR23B protein.We prepared various internal as well as terminal deletion products of hHR23B protein in a His-tagged form and examined their binding with rhXPC by using nickel-chelating Sepharose. We demonstrate that a domain covering 56 amino acids of hHR23B is required for binding to rhXPC as well as for stimulation of in vitro NER reactions. Interestingly, a small polypeptide corresponding to the XPC-binding domain is sufficient to exert stimulation of XPC NER activity. Comparison with known crystal structures and analysis with secondary structure programs provided strong indications that the binding domain has a predominantly amphipathic ␣-helical character, consistent with evidence that the affinity with XPC is based on hydrophobic interactions. Our work shows that binding to XPC alone is required and sufficient for the role of hHR23B in in vitro NER but does not rule out the possibility that the protein has additional functions in vivo.

Constant Cyclin B levels are maintained during a CSF arrest through the regulation of Emi2 activity. A balance between Cdc2 and PP2A controls Emi2 phosphorylation, which in turn controls the ability of Emi2 to bind to and inhibit the APC. This balance allows proper maintenance of Cyclin B levels and Cdc2 kinase activity during CSF arrest.

Defects in the human gene XPV result in the variant form of the genetic disease xeroderma pigmentosum (XP-V). XPV encodes DNA polymerase eta, a novel DNA polymerase that belongs to the UmuC/DinB/Rad30 superfamily. This polymerase catalyzes the efficient and accurate translesion synthesis of DNA past cis-syn cyclobutane di-thymine lesions. In this report we present the cDNA sequence and expression profiles of the mouse XPV gene and demonstrate its ability to complement defective DNA synthesis in XP-V cells. The mouse XPV protein shares 80.3% amino acid identity and 86.9% similarity with the human XPV protein. The recombinant mouse XPV protein corrected the inability of XP-V cell extracts to carry out DNA replication, by bypassing thymine dimers on template DNA. Transfection of the mouse or human XPV cDNA into human XP-V cells corrected UV sensitivity. Northern blot analysis revealed that the mouse XPV gene is expressed ubiquitously, but at a higher level in testis, liver, skin and thymus compared to other tissues. Although the mouse XPV gene was not induced by UV irradiation, its expression was elevated approximately 4-fold during cell proliferation. These results suggest that DNA polymerase eta plays a role in DNA replication, though the enzyme is not essential for viability.