The nuclear protein in testis gene (i.e. NUTM1 gene) encodes (i.e. directs the synthesis of) a 1,132-amino acid protein termed NUT that is expressed almost exclusively in the testes, ovaries, and ciliary ganglion (i.e. a parasympathetic ganglion of nerve cells located just behind the eye). NUT protein facilitates the acetylation of chromatin (i.e. DNA-protein bundles) by histone acetyltransferase EP300 in testicular spermatids (cells that mature into sperms). This acetylation is a form of chromatin remodeling which compacts spermatid chromatin, a critical step required for the normal conduct of spermatogenesis, i.e. the maturation of spermatids into sperm. Male mice that lacked the mouse Nutm1 gene using a gene knockout method had abnormally small testes, lacked sperm in their cauda epidid