Nucleotide sequence of cDNA and derived amino acid sequence of human complement component C9.

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Abstract
The nucleotide sequence coding for the ninth component of human complement (C9) was determined and the corresponding amino acid sequence was derived. A human liver cDNA [complementary DNA] library was screened by the colony-hybridization technique using 2 radiolabeled oligonucleotide probes that correspond to known regions of the C9 amino acid sequence. Two recombinant plasmids were isolated and their cDNA inserts were sequenced. The derived protein sequence consists of 537 amino acids in a single polypeptide chain. A profile of the hydropathic index vs. sequence number indicates that the amino-terminal half of the C9 is predominantly hydrophilic in character whereas the carboxyl-terminal section of this protein is more hydrophobic. The amphipathic organization of the primary structure of C9 is consistent with the known potential of polymerized C9 to penetrate lipid bilayers, causing the formation of transmembrane channels.