Authors Liyun Liu and Woody Hastings
Dinoflagellates are an unusual group of organisms in many respects, including a large amount of DNA per cell (up to 40x that of the human) and the ancestral diversity of their genes. In bioluminescent species light is emitted from small (0.4um) cell organelles, which in Lingulodinium polyedrum contain two proteins involved in light emission: dinoflagellate luciferase (LCF) and a substrate (luciferin)-binding protein (LBP). Both proteins are unusual in that they have internal repeat-sequence domains, three for LCF and four in the case of LBP. In the case of LCF, each of the domains is separately active as an enzyme in the reaction.
In this paper we report that in a more primitive species these two functions occur in a single protein encoded by a single gene. The luciferase function occurs as only a single domain, homologous to but shorter than those of L. polyedrum, while the luciferin binding sequence is about the same length as that from L. polyedrum with four domains.
The evolution of genes for light emission might have involved either fusion or fission. Thus, the ancestral system may have had two genes, which fused in the Noctiluca lineage but remained separate in the branch leading to the photosynthetic species. Alternatively, based on the more primitive status of Noctiluca, its luciferase gene can be viewed as similar to the ancestral gene in dinoflagellates, which then split in giving rise to L. polyedru.
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