Molecular cloning of the rat complement regulatory protein, 5I2 antigen

We have cloned a cDNA which encoded for rat complement regulatory protein, 5I2 antigen. The deduced amino acid sequence of 497 residues predicted essentially the same domain structure as the mouse complement regulatory protein, Crry/p65, composed of five short consensus repeat (SCR) domains, a transmembrane domain and a cytoplasmic domain. 5I2 antigen, however, had an additional SCR which showed a close similarity to the sixth SCR of mouse complement receptor 1 (CR1) or to the sixth, thirteenth, twentieth and twenty seventh SCR of human CR1. Corresponding domains of 5I2 antigen and mouse Crry/p65 showed 70%-86% amino acid identity, indicating that 5I2 antigen is the rat counterpart of mouse Crry/p65.