The RAD4 gene which is required for the incision of UV-induced excision repair in Saccharomyces cerevisiae has been cloned. A 7.6kb positive clone containing the RAD4 gene was isolated from a yeast genomic library by complementation of a UV-sensitive rad4-4 mutant and further narrowed down to 2.6kb by trimming with BglII-BamHI. This plasmid appeared to complement the rad4-3 and rad4-4 mutants. We were able to propagate the functional RAD4 gene via E. coli host in contrast to the results of Fleer et al. This gene was not a supressor gene but a truly functional RAD4 gene as determined by hybridization of 5′-end-labled yeast tRNA probe. The RAD4 gene seemed to be nonessential for the yeast viability. When yeast cells were exposed to UV light as DNA damaging agent, we could not observe the increase of RAD4 gene transcription suggesting that it is not an inducible gene. The RNA transcript size was found to be 2.3kb and 1.2kb as determined by Northern hybridization. The size of RAD4 gene product determined by SDS-PAGE was approximately 89kd.