title: Repair of abasic sites by mammalian cell extracts.
abstract: Hamster cell extracts that perform repair synthesis on covalently closed circular DNA containing pyrimidine dimers, were used to study the repair of apurinic/apyrimidinic (AP) sites and methoxyamine (MX)-modified AP sites. Plasmid molecules were heat-treated at pH 5 and incubated with MX when required. The amount of damage introduced ranged from 0.2 to 0.9 AP sites/kb. Extracts were prepared from the Chinese hamster ovary CHO-9 cell line and from its derivative, 43-3B clone which is mutated in the nucleotide excision repair (NER) ERCC1 gene. AP and MX-AP sites stimulated repair synthesis by CHO-9 cell extracts. The level of synthesis correlated with the number of lesions and was of similar magnitude to the repair stimulated by 4.3 u.v. photoproducts/kb. Repair of AP and MX-AP sites was faster than the repair of u.v. damage and was independent of ERCC1 gene product. The high level of repair replication was due to a very efficient and rapid incision of plasmids carrying AP or MX-AP sites, performed by abundant AP endonucleases present in the extract. The calculated average repair patch sizes were: 7 nucleotides per AP site; 10 nucleotides per MX-AP site; 28 nucleotides per (6-4) u.v. photoproduct or cyclobutane pyrimidine dimer. The data indicate that AP and MX-AP sites are very efficiently repaired by base-excision repair in mammalian cells and suggest that MX-AP sites may also be processed via alternative repair mechanisms.
authors: Laboratory of CSTA-Mutagenesis, Istituto Nazionale per la Ricerca sul Cancro, IST, Genova, Italy.
authors: G
authors: G
authors: Frosina
authors: P
authors: P
authors: Fortini
authors: O
authors: O
authors: Rossi
authors: F
authors: F
authors: Carrozzino
authors: A
authors: A
authors: Abbondandolo
authors: E
authors: E
authors: Dogliotti
mesh_terms: D000818:Animals; D001080:Apurinic Acid / Q000378:metabolism*; D016466:CHO Cells; D002457:Cell Extracts / Q000494:pharmacology*; D002474:Cell-Free System; D006224:Cricetinae; D004260:DNA Repair; D004261:DNA Replication; D004270:DNA, Circular / Q000096:biosynthesis / Q000378:metabolism*; D004278:DNA, Superhelical / Q000096:biosynthesis / Q000378:metabolism; D006898:Hydroxylamines / Q000378:metabolism / Q000494:pharmacology; D009711:Nucleotides / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011119:Polynucleotides / Q000378:metabolism*; D013268:Stimulation, Chemical; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D002457:Cell Extracts; D004270:DNA, Circular; D004278:DNA, Superhelical; D006898:Hydroxylamines; D009711:Nucleotides; D011119:Polynucleotides; C001790:apyrimidinic acid; D001080:Apurinic Acid; C005214:methoxyamine