Molecular cloning of the seventh component of complement in rainbow trout.

C7 is an integral component of the lytic pathway of complement, which interacts in a sequence of polymerization reactions with other terminal components to form the membrane attack complex. C7 plays a central role in the terminal complement cascade, since its incorporation into the nascent complex allows its hydrophilic-amphiphilic transition, which subsequently leads to the direct binding of the complex to the target membrane. To date, only human and porcine C7 have been cloned and characterized. Here we report the isolation of a C7 molecule from the rainbow trout (Oncorhynchus mykiss). The full-length trout C7 cDNA was isolated, and the predicted amino acid sequence exhibits 44 and 65% identity with human and Japanese flounder C7, respectively. The cysteine backbone and two putative N-linked glycosylation sites are conserved in trout C7. It also contains the same structural motifs as those found in mammalian C7. Trout C7 mRNA expression was detected in all tissues investigated, except kidney and spleen.