RESUMEN
Xeroderma pigmentosum complementation group G (XPG) protein is a junction-specific endonuclease which is indispensable for nucleotide excision repair (NER) of DNA in eukaryotes. Recent studies have hinted at a second, essential function for the XPG protein in higher eukaryotes. We undertook a comparison of the amino acid sequences of multiple XPG orthologs to determine if a motif or domain could be identified that is conserved uniquely in higher eukaryotes. A search of current databases allowed us to retrieve complete amino acid sequences for the human, mouse and Xenopus XPG proteins, and for two yeast orthologs. We also identified an incomplete Drosophila open reading frame (ORF) that was a good candidate for the XPG protein. We cloned a complete Drosophila cDNA for this ORF and examination of the primary amino acid sequence suggests that this cDNA encodes the Drosophila ortholog of XPG. A comparison of all six orthologous polypeptides reveals the presence of two previously unidentified conserved domains. One of these is unique to all four higher eukaryotic sequences. Conceivably this domain evolved to support the essential function of XPG protein.
Asunto(s)
Proteínas de Unión al ADN/genética , Drosophila melanogaster/genética , Secuencia de Aminoácidos , Animales , Línea Celular , Clonación Molecular , Secuencia Conservada/genética , ADN/química , ADN/genética , ADN Complementario/química , ADN Complementario/genética , Drosophila melanogaster/química , Endonucleasas , Células Eucariotas/metabolismo , Humanos , Datos de Secuencia Molecular , Proteínas Nucleares , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Factores de TranscripciónRESUMEN
Mice that are genetically engineered to mimic the human hereditary cancer-prone DNA repair-defective disease xeroderma pigmentosum (XP) are highly predisposed to UV radiation-induced skin cancer. It is not clear, however, whether XP mice or humans are predisposed to cancers in other tissues associated with exposure to environmental carcinogens. To test the importance of nucleotide excision repair in protection against chemical carcinogenesis in internal organs, we treated XPC mutant (XPC-/-) mice with 2-acetylaminofluorene and NOH-2-acetylaminofluorene. We observed a significantly higher incidence of chemically induced liver and lung tumors in XPC-/- mice compared with normal and heterozygous littermates In addition, the progression of liver tumors in XPC-/- Trp53+/- mice is accelerated compared with XPC-/- Trp53+/+ animals. Finally, we demonstrate a higher incidence of spontaneous testicular tumors in XPC-/- TrpS3-/- double mutant mice compared with XPC+/+ Trp53-/- mice.
Asunto(s)
2-Acetilaminofluoreno/toxicidad , Reparación del ADN/genética , Genes p53/fisiología , Neoplasias Hepáticas Experimentales/inducido químicamente , Neoplasias Pulmonares/inducido químicamente , Neoplasias Testiculares/etiología , Xerodermia Pigmentosa/genética , Animales , Femenino , Humanos , Masculino , Ratones , Ratones Endogámicos C57BL , MutaciónRESUMEN
The hereditary disease Cockayne syndrome (CS) is a complex clinical syndrome characterized by arrested post-natal growth as well as neurological and other defects. The CSA and CSB genes are implicated in this disease. The clinical features of CS can also accompany the excision repair-defective hereditary disorder xeroderma pigmentosum (XP) from genetic complementation groups B, D or G. The XPB and XPD proteins are subunits of RNA polymerase II (RNAP II) transcription factor IIH (TFIIH). We show here that extracts of CS-A and CS-B cells, as well as those from XP-B/CS cells, support reduced levels of RNAP II transcription in vitro and that this feature is dependent on the state or quality of the template.
