The prototypic acute-phase protein, CRP, is an evolutionarily conserved protein present both in mammals and the invertebrate Limulus Polyphemus. To gain further insight into the biological function, mode of production and evolution of CRPs, studies with Xenopus laevis was carried out. CRP was isolated from Xenopus laevis and its amino-terminal sequence determined. Based on this information and the conserved sequence around the putative calcium binding region, and 1.0 kb cDNA clone coding for the entire Xenopus laevis CRP was isolated and sequenced. Subsequently, the CRP gene was also isolated and characterized. RNA blot analysis indicated that the Xenopus CRP is about 1.0 kb in size. Analyses of the protein and nucleotide sequences revealed that the mature CRP in a 222-amino acid protein preceded by a 16-residue signal peptide. The mature human and Xenopus CRPs share 45% identity. Within the sequences of all known CRPs from different species, there are several stretches of highly conserved regions. One of which in the site proposed an the phosphocholine (PC)-binding region. However, the basic amino acids proposed to be important for PC-binding are missing in the Xenopus CRP indicating that either this region is not involved in PC-binding or more likely, that PC-binding does not require positively charged amino acids in this region. Significant differences between human and Xenopus CRP genes were noted. The heatshock consensus sequence and the Interleukin-6 responsible elements found in the 5' end of the human CRP gene are not present in the Xenopus CRP gene. By RNA and western blot analyses, we have shown that Xenopus CRP gone in not up-regulated during inflammation and is expressed as liver matures but not during early development.
