The gene, designated MNS1, encodes a 549-amino acid polypeptide of calculated molecular size 63,017 Da produced by an mRNA species of approximately 1.7 kilobases. The protein possesses a putative non-cleavable signal sequence near its N-terminal region which probably acts as a transmembrane domain. It has three potential N-glycosylation sites and a calcium-binding consensus sequence. MNS1 (meiosis-specific nuclear structural protein 1) is necessary for motile cilia function, such as sperm flagella or those found in the embryonic primitive node. MNS1 is expressed in the germ cells in the testes and localizes to sperm flagella in a detergent-resistant manner, indicating that it is an integral component of flagella. MNS1-deficient males are sterile, as they exhibit a sharp reduction in sperm production and the remnant sperm are immotile with abnormal short tails. MNS1 is essential for spermiogenesis, the assembly of sperm flagella, and motile ciliary functions.