PTOV1 was predicted to form alternating alpha helices and beta sheets. Normal prostate expressed low PTOV1 levels. Western blot analysis of prostate tumor tissue detected PTOV1 at an apparent molecular mass of 58 kD. Immunocytochemical analysis detected endogenous PTOV1 in the cytoplasm, concentrated around the nucleus.PTOV1 was overexpressed in 71% of 38 prostate carcinomas and in 80% of samples with prostate intraepithelial neoplasia. High levels of PTOV1 in tumors correlated significantly with proliferative index and localization of PTOV1 in the nucleus. In quiescent cultured prostate tumor cells, PTOV1 localized to the cytoplasm and was excluded from nuclei. After serum stimulation, PTOV1 partially translocated to the nucleus at the beginning of S phase.