iiolot/ical Science. Floriilii Slute ['nii'crsity, 'I'ulliiliussci'. Florida 32306 Coelenterates have long been considered primitive or simple animals. Although some aspects have heen known for a long time, coelenterate behavior and its physiological and morphological bases are still poorly understood. Studies have now

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C3, C4, and C5 are thiolester-containing proteins (TEPs) of vertebrate complement. The identification of the molecular origin of the TEP family, and more specifically the ancestor protein of complement components C3, C4, and C5, remains a fundamental question. The prevailing paradigm suggests that duplication and divergence of these proteins occurred after the deuterostome split in phylogeny. It is believed that the ancestor of thiolester-containing complement proteins was alpha-2-macroglobulin (A2M)-like, a noncomplement-related protein. Here we describe a C3-like cDNA from a gorgonian coral, Swiftia exserta. This study provides evidence for the origins of a complement-related C3-like gene in the Precambrian period, predating both protostomes and deuterostomes. Furthermore, one may speculate that complement-like opsonic reactions were evolving at the earliest stages of metazoan evolution. This calls for a reassessment of the present concepts concerning the origins and evolution of TEPs.

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