Microinjection of human cell extracts corrects xeroderma pigmentosum defect.

The EMBO Journal (Impact Factor: 10.43). 02/1983; 2(5):637-41.
Source: PubMed


Cultured fibroblasts of patients with the DNA repair syndrome xeroderma pigmentosum (XP) were injected with crude cell extracts from various human cells. Injected fibroblasts were then assayed for unscheduled DNA synthesis (UDS) to see whether the injected extract could complement their deficiency in the removal of u.v.-induced thymidine dimers from their DNA. Microinjection of extracts from repair-proficient cells (such as HeLa, placenta) and from cells belonging to XP complementation group C resulted in a temporary correction of the DNA repair defect in XP-A cells but not in cells from complementation groups C, D or F. Extracts prepared from XP-A cells were unable to correct the XP-A repair defect. The UDS of phenotypically corrected XP-A cells is u.v.-specific and can reach the level of normal cells. The XP-A correcting factor was found to be sensitive to the action of proteinase K, suggesting that it is a protein. It is present in normal cells in high amounts, it is stable on storage and can still be detected in the injected cells 8 h after injection. The microinjection assay described in this paper provides a useful tool for the purification of the XP-A (and possibly other) factor(s) involved in DNA repair.

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Available from: Wim Vermeulen
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    ABSTRACT: An assay has been developed in which excision repair deficiency of xeroderma pigmentosum cells is transiently complemented, as measured by unscheduled DNA synthesis, by microinjection of cytoplasmic poly(A)+ RNA derived from HeLa cells. Four different complementation groups of xeroderma pigmentosum have been assayed. Groups A and G showed complementation, whereas groups D and F did not. Survival for cells in each of the groups subsequent to microinjection was approximately equal to 75%. Approximately 10-25% of surviving cells from groups A and G were complemented, as judged by near-normal unscheduled DNA synthesis. Fractionation of cytoplasmic poly(A)+ RNA on a 15-30% nondenaturing sucrose gradient and subsequent microinjection of the individual fractions indicate that repair mRNAs that complement xeroderma pigmentosum groups A and G sediment at approximately 11 S and 12 S, respectively. This assay should be of great utility in the cloning and biochemical analysis of DNA repair genes.
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