Abstract
Murine fourth component of complement (C4) and sex-limited protein (Slp) are 2 closely related serum proteins whose structural genes lie in the S region of the murine H-2 complex. Two very similar (95% nucleotide sequence identity) c[complementary]DNAs were cloned; they encode amino acid sequences that are distinct but that correspond equally well with the limited amino acid sequence available for murine and human C4. One of these was identified as C4 cDNA and the other as Slp cDNA by comparing, in a RNA blot hybridization experiment, the extent of hybridization of the 2 cDNAs to liver mRNAs from inbred mouse strains expressing varying amounts of C4 and Slp proteins in their plasma. The C4 and Slp cDNAs were used in a Southern blot experimental to identify the C4 and Slp genes in the molecular map of the S region.