Expression of the midnolin gene is developmentally regulated: it is strongly expressed at the mesencephalon (midbrain) of the embryo in day 12.5 (E12.5) mice. The midnolin encodes a protein of 508 amino acids (aa), which contains a Ubiquitin-like domain. The intracellular distribution of the midnolin was studied by using midnolin-green fluorescent protein (GFP) fusion proteins. Midnolin was found to be localized in the nucleus and nucleolus, but not in the cytoplasm. The nucleolar localization signal was determined to be a 28aa peptide located at the C-terminal region of the midnolin. May be involved in regulation of genes related to neurogenesis in the nucleolus.