Male germ-cell putative homeodomain transcription factor
This domain is found in bacteria and eukaryotes, and is typically between 101 and 140 amino acids in length. Phtf proteins do not display any sequence similarity to known or predicted proteins, but their conservation among species suggests an essential function. The 84 kDa Phtf1 protein is an integral membrane protein, anchored to a cell membrane by six to eight trans-membrane domains, that is associated with a domain of the endoplasmic reticulum (ER) juxtaposed to the Golgi apparatus. It is present during meiosis and spermiogenesis, and, by the end of spermiogenesis, is released from the mature spermatozoon within the residual bodies. Phtf1 enhances the binding of FEM1B -feminisation homolog 1B - to cell membranes. Fem-1 was initially identified in the signaling pathway for sex determination, as well as being implicated in apoptosis, but its biochemical role is still unclear, and neither FEM1B nor PHTF1 is directly implicated in apoptosis in spermatogenesis. It is the ANK domain of FEM1B that is necessary for the interaction with the N-terminal region of Phtf1.