UV-irradiation induces, in mammalian cells, the expression of a set of genes known as the 'UV-response', which may be reminiscent of the bacterial response, called SOS system. The multifunctional protein RecA controls the expression of the SOS genes. We report the expression profile of a mouse gene conserved among mammals, called Kin17, that codes a DNA-binding protein of undetermined biochemical activity and which shares epitopes with the bacterial RecA protein. We demonstrate that the level of Kin17 RNA was 5-fold higher in mid-S phase of serum-stimulated BALB/c 3T3 fibroblasts than in quiescent cells. Cells in S-phase displayed a high level of kin17 protein with a marked nuclear localisation. The maximal level of Kin17 RNA was observed 18 h after serum stimulation, indicating that Kin17 gene is a new member of the late growth-related genes. The accumulation of kin17 protein during cell proliferation follows the increase in Kin17 RNA and correlates with DNA synthesis, which suggests a possible role of kin17 protein in a transaction related to DNA-replication. In quiescent fibroblasts, a 3-fold increase in Kin17 RNA was seen 13 h after UV irradiation. In parallel, kin17 protein accumulated in the nucleus, which suggests that it might be required after the stress produced by UV irradiation.