Functional complementation of xeroderma pigmentosum complementation group E by replication protein A in an in vitro system.
Proc Natl Acad Sci U S A
; 93(10): 5014-8, 1996 May 14.
Article
in En
| MEDLINE
| ID: mdl-8643521
ABSTRACT
Xeroderma pigmentosum (XP) is caused by a defect in nucleotide excision repair. Patients in the complementation group E (XP-E) have the mildest form of the disease and the highest level of residual repair activity. About 20% of the cell strains derived from XP-E patients lack a damaged DNA-binding protein (DDB) activity that binds to ultraviolet-induced (6-4) photoproducts with high affinity. We report here that cell-free extracts prepared from XP-E cell strains that either lacked or contained DDB activity were severely defective in excising DNA damage including (6-4) photoproducts. However, this excision activity defect was not restored by addition of purified DDB that, in fact, inhibited removal of (6-4) photoproducts by the human excision nuclease reconstituted from purified proteins. Extensive purification of correcting activity from HeLa cells revealed that the correcting activity is inseparable from the human replication/repair protein A [RPA (also known as human single stranded DNA binding protein, HSSB)]. Indeed, supplementing XP-E extracts with recombinant human RPA purified from Escherichia coli restored excision activity. However, no mutation was found in the genes encoding the three subunits of RPA in an XP-E (DDB-) cell line. It is concluded that RPA functionally complements XP-E extracts in vitro, but it is not genetically altered in XP-E patients.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Main subject:
Xeroderma Pigmentosum
/
DNA-Binding Proteins
Limits:
Humans
Language:
En
Journal:
Proc Natl Acad Sci U S A
Year:
1996
Document type:
Article
Affiliation country:
United States