NOVEL AND RAPIDLY DIVERGING INTERGENIC SEQUENCES BETWEEN TANDEM REPEATS OF THE LUCIFERASE GENES IN SEVEN DINOFLAGELLATE SPECIES1

Abstract

Tandemly arranged luciferase genes were previously reported in two dinoflagellates species, but their intergenic regions were strikingly different and no canonical promoter sequences were found. Here, we examined the intergenic regions of the luciferase genes of five other dinoflagellate species along with those of the earlier two. In all cases, the genes exist in multiple copies and are arranged tandemly, coding for proteins of similar sizes and sequences. However, the 5′ untranslated region, 3′ untranslated region, and intergenic regions of the seven genes differ greatly in length and sequence, except for two stretches that are conserved in the intergenic regions of two pairs of phylogenetically close species. Microsatellites and minisatellites were detected in the intergenic sequences of four species, Alexandrium affine (H. Inoue & Y. Fukuyo) E. Balech, A. tamarense (Lebour) E. Balech, Protoceratium reticulatum (Claparède & Lachmann) Butschli, and Pyrocystis lunula (Schütt) Schütt, the first three of which have unusually high percentages of particular sets of dinucleotides. Most remarkably, the P. reticulatum intergenic region is almost exclusively made up of 19 nearly identical repeats of an 11‐nucleotide sequence. Dinoflagellate luciferase intergenic regions bear similarities to ribosomal genes and to some protein‐encoding genes in trypanosomes, both of which are transcribed by RNA polymerase I. It is possible that the transcription of the dinoflagellate genes are catalyzed by an RNA polymerase with novel properties.