CHARACTERIZATION OF XENOPUS-LAEVIS COMPLEMENT FACTOR-I STRUCTURE-CONSERVATION OF MODULAR STRUCTURE EXCEPT FOR AN UNUSUAL INSERT NOT PRESENT IN HUMAN FACTOR-I

Factor I (C3b/C4b inactivator) is a regulatory protein of the classical and alternative complement pathways. In this paper, we report the sequence of Xenopus factor I cDNA and the deduced protein structure. The basic structure of human preprofactor I, NH2-heavy chain-cleavage peptide-light chain-COOH, is conserved in the frog. However, the frog heavy chain contains a highly charged segment of 29 amino acids, encoded by a poly dA-rich mRNA insert, which is not found in human factor I. The modular structure of the frog heavy chain was analyzed, and found to differ vis-a-vis previously published analyses of human factor I. We also evaluate the timing of factor I transcription during frog embryogenesis.