mRNA from the dinoflagellate Symbiodinium sp. isolated from the staghorn coral Acropora formosa was used for the construction of cDNA libraries. A cDNA clone was identified which encoded the precursor of peridinin-chlorophyll a-binding protein (PCP), including a 52 amino acid transit peptide and the 313 amino acid mature protein. The deduced amino acid sequence clearly contains an internal duplication, implying that amongst dinoflagellates the M(r) 35,000 form of PCP has arisen by duplication and fusion of genes encoding the M(r) 15,000 form. This is the first reported sequence of a dinoflagellate light-harvesting protein. The anatomy of the mature protein and the transit peptide are discussed.