Complex gene structure of the form II RUBISCO in the dinoflagellate Prorocentrum minimum (Dinophyceae)

We analyzed the unusually complex organization of the nuclear-encoded (form II) RUBISCO gene in the dinoflagellate Prorocentrum minimum (Parvillard) Schiller by intensive genomic DNA and cDNA sequencing and Western blotting. Over 10 transcribed units (TUs) were detected, which varied dramatically in their 3' untranslated region. Each TU appeared to contain four tandem copies of the RUBISCO coding region (1.46 kb each; coding unit, or CU) interspersed by a 63-bp spacer; the four CUs in each TU were cotranscribed and apparently cotranslated to a tetrameric polyprotein that may undergo successive cleavage steps to yield mature RUBISCO. By means of real-time PCR analysis, it was estimated that each of the P. minimum genome harbored 148+/-16 CUs. Although nucleotide sequences varied by 1%-9% among the detected CUs, their inferred amino acid sequences were essentially identical. Our results suggest that the complex structure of Pmrbc has been derived from extensive and repeated gene duplications, an evolutionary process that has also been observed for other dinoflagellate genes.