Gene duplication of the seventh component of complement in rainbow trout.

The seventh component of complement is a single-chain plasma glycoprotein that is involved in the cytolytic phase of complement activation through a sequence of polymerization reactions with other terminal components. We have previously isolated and characterized a C7 gene in rainbow trout (Oncorhynchus mykiss). Here, we report the cloning of a second trout C7 gene (C7-2). The deduced amino acid sequence of the C7-2 gene exhibits 43 and 50% identity with human C7 and trout C7-1, respectively. The structural motifs of trout C7-2 resemble those of mammalian C7 more than trout C7-1, and the cysteine backbone shows a high degree of conservation. C7-2 presents a different tissue expression profile from trout C7-1, which correlates with that of mammalian counterparts. Although duplication of complement genes is a common observation in teleost fish, this is the first report of two gene isotypes of a terminal membrane attack complex/perforin complement component in any organism.