We completed the cDNA cloning and sequencing of gp330, the major kidney glomerular antigen for rat Heymann nephritis. However, gp330 differs from these proteins in (i) the cysteine-rich repeat arrangements found in the extreme extraceilular N-and C-terminal regions, (ii) the distribution pattern of cysteine residues in the YWTD spacer regions, (Mi") the location of the RX(K/R)R consensus recognition sequence offurin, a precursor processing endoprotease, and (iv) the length and rutrof the cytoplasmic tail. We suggest the name megaliln (from Greek mega) for gp330, the largest plasma membrane proti Identified so far in vertebrates. The cloned cDNA will be useful for studies on the physiological functions of gp330/megalin and for determining its role in Heymann nephritis.