This family contains several eukaryotic transmembrane proteins which are homologous to human transmembrane protein 9. The TMEM9 gene encodes a 183 amino-acid protein that contains an N-terminal signal peptide, a single transmembrane region, three potential N-glycosylation sites and three conserved cys-rich domains in the N-terminus, but no known functional domains. The protein is highly conserved between species from Caenorhabditis elegans to man and belongs to a novel family of transmembrane proteins. The exact function of TMEM9 is unknown although it has been found to be widely expressed and localized to the late endosomes and lysosomes. Members of this family contain pfam03128 repeats in their N-terminal region.