Abstract
Dinoflagellates are unicellular protists that feature a multitude of unusual nuclear features, including large genomes, packaging of DNA without histones, and multiple gene copies organized as tandem gene arrays. Furthermore, all dinoflagellate mRNAs experience trans-splicing with a common 22-nucleotide splice leader (SL) sequence. These features challenge some of the concepts and assumptions about the regulation of gene expression derived from work on model eukaryotes such as yeasts and mammals. Translational control in the dinoflagellates, based on extensive study of circadian bioluminescence and by more recent microarray and transcriptome analyses, is now understood to be a crucial element in regulating gene expression. A picture of the translation machinery of dinoflagellates is emerging from the recent availability of transcriptomes of multiple dinoflagellate species and the first complete genome sequences. The components comprising the translational control toolkit of dinoflagellates are beginning to take shape and are outlined here.
Highlights
Dinoflagellates are a diverse group of unicellular protists that exhibit a great range of size, form and lifestyle
Translation initiation refers to the formation of translation-competent ribosomes, where the initiator tRNA (Met-tRNAi) in the ribosomal P-site is base-paired to the mRNA start codon
The identity of the cap structure for dinoflagellate transcripts needs to be determined, but there are more possibilities than the monomethylated m7GTP typically found on mRNA or the trimethylguanosine found on small nuclear RNAs
Summary
Dinoflagellates are a diverse group of unicellular protists that exhibit a great range of size, form and lifestyle. The dinoflagellates all contain alveoli, flattened membrane bound compartments of unknown function lying underneath the plasma membrane, that has given rise to the name alveolata They share a number of unusual nuclear characteristics including generally high DNA content, numerous chromosomes that remain condensed during interphase, DNA in a liquid crystal structure without observable nucleosomes and DNA in which 5-hydroxymethyluracil replaces some of the thymine [9,10,11]. As a consequence of these latter substitutions, the protein-DNA ratio in core dinoflagellates is much lower than in syndinians, such as Hematodinium spp, which were previously considered more like typical eukaryotes because of their lower chromosome number, smaller genomes and no obvious gene amplification [16,28]. Both transcriptomic [20] and genomic [17] analyses have shown there is a paucity of sequence-specific transcription factors in dinoflagellates, consistent with constant, steady transcription of most genes with fewer genes under sequence-specific transcriptional control
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