Regional mapping of the X-linked gene for a human cell surface antigen, SA-X

The presence of the SA-X gene on the long arm is consistent with the fact that the antiserum is made with a hybrid presumed to contain only the long arm of the X. Another anti-SA-X serum has been made with a human-mouse hybrid that expresses only human G6PD and not HPRT or PGK. This is consistent with the localization of the SA-X gene in a region of the X chromosome adjacent to G6PD and distal to HPRT. Since the assignment of the X-linked blood group Xg(a) to the short arm of the X chromosome is not confirmed, the possibility remains that SA-X is related to Xg, perhaps being a species-specific part of the Xg molecule.