Expression of an excision repair gene in transformation of Bacillus subtilis.

DNA of Bacillus subtilis proficient in excision repair (hcr+) was introduced into Angiografinpurified competent cells of an excision repair-deficient strains UVS-1 (hcr-1). The hcr+ gene was found to affect the UV-survival curve of the cells, giving rise to a UV-resistant component. However, a considerable number of colonies of the UV-resistant component consisted of cells that were not transformed to hcr+ as judged by their sensitivity to mitomycin C (MC), UV, and by their ability to reactivate UV-irradiated M2 phages. This suggests that the hcr gene may be expressed without integration. The recA function of B. subtilis was necessary for expression of UV resistance to occur. When DNA-treated cells were selected for met+ recombinants, the UV-resistant component was again found on the UV-survival curve and about half of the colonies of the UV-resistant component consisted of Hcr- cells. This result was explained by an integration-segregation model for hcr+ and met+ genes. The effect of the hcr+ gene was seen even when DNA was added after cells were irradiated with UV, although this effect was gradually diminished by delaying the time of DNA addition. A complementation effect was found between two excision repair mutations residing in two distant loci, using hcr-114 DNA as a donor and hcr-1 cells as a recipient.