A new class of transcription initiation factors, intermediate between TATA box-binding proteins (TBPs) and TBP-like factors (TLFs), is present in the marine unicellular organism, the dinoflagellate Crypthecodinium cohnii.
Dinoflagellates are marine unicellular eukaryotes that exhibit unique features including a very low level of basic proteins bound to the chromatin and the complete absence of histones and nucleosomal structure. A cDNA encoding a protein with a strong homology to the TATA box-binding proteins (TBP) has been isolated from an expressed sequence tag library of the dinoflagellate Crypthecodinium cohnii. The typical TBP repeat signature and the amino acid motives involved in TFIIA and TFIIB interactions were conserved in this new TBP-like protein. However, the four phenylalanines known to interact with the TATA box were substituted with hydrophilic residues (His(77), Arg(94), Tyr(171), Thr(188)) as has been described for TBP-like factors (TLF)/TBP-related proteins (TRP). A phylogenetic analysis showed that cTBP is intermediate between TBP and TLF/TRP protein families, and the structural similarity of cTBP with TLF was confirmed by low affinity binding to a consensus' TATA box in an equivalent manner to that usually observed for TLFs. Six 5'-upstream gene regions of dinoflagellate genes have been analyzed and neither a TATA box nor a consensus-promoting element could be found within these different sequences. Our results showed that cTBP could bind stronger to a TTTT box sequence than to the canonical TATA box, especially at high salt concentration. Same binding results were obtained with a mutated cTBP (mcTBP), in which the four phenylalanines were restored. To our knowledge, this is the first description of a TBP-like protein in a unicellular organism, which also appears as the major form of TBP present in C. cohnii.
Guillebault
Delphine
D
Observatoire océanologique, laboratoire Arago, UMR 7628 CNRS-Université Paris VI, BP 44, F-66651 Banyuls-sur-mer cedex, France.
Sasorith
Souphatta
S
Derelle
Evelyne
E
Wurtz
Jean-Marie
JM
Lozano
Jean-Claude
JC
Bingham
Scott
S
Tora
Laszlo
L
Moreau
Hervé
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017931:DNA Primers; D004141:Dinoflagellida / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*
D017931:DNA Primers; D014157:Transcription Factors