Molecular and Cellular Biology, November 2001, p. 7872-7882, Vol. 21, No. 22
Department of Microbiology, Immunology, and
Molecular Genetics,1 Molecular Biology
Institute,2 and Howard Hughes Medical
Institute,3 University of California, Los
Angeles School of Medicine, Los Angeles, California 90095-1489
Received 7 June 2001/Returned for modification 4 August
2001/Accepted 17 August 2001
While considerable progress has been made in understanding the
mechanisms of transcription in higher eukaryotes, transcription in
single-celled, primitive eukaryotes remains poorly understood. Promoters of protein-encoding genes in the parasitic protist
Trichomonas vaginalis, which represents one of the
deepest-branching eukaryotic lineages, have a bipartite structure with
gene-specific regulatory elements and a conserved core promoter
encompassing the transcription start site. Core promoters in T.
vaginalis appear to consist solely of a highly conserved
initiator (Inr) element that is both a structural and a functional
homologue of its metazoan counterpart. Using DNA affinity
chromatography, we have isolated an Inr-binding protein from T.
vaginalis. Cloning of the gene encoding the Inr binding protein
identified a novel 39-kDa protein (IBP39). We show that IBP39 binds to
both double and single Inr motifs found in T. vaginalis genes and that binding requires the conserved nucleotides necessary for
Inr function in vivo. Analyses of the cloned IBP39 gene revealed no
homology at the protein sequence level with identified proteins in
other organisms or the presence of known DNA-binding domains. The
relationship between IBP39 and Inr-binding proteins in metazoa presents
interesting evolutionary questions.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.22.7872-7882.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Initiator Recognition in a Primitive Eukaryote:
IBP39, an Initiator-Binding Protein from Trichomonas
vaginalis

*
Corresponding author. Mailing address: Department of
Microbiology, Immunology, and Molecular Genetics, UCLA School of
Medicine, 405 Hilgard Ave., 1602 Molecular Sciences Bldg., Los Angeles, CA 90095-1489. Phone: (310) 825-4870. Fax: (310) 206-5231. E-mail: johnsonp{at}ucla.edu.
Present address: Section of Microbial Pathogenesis, Boyer Center
for Molecular Medicine, Yale University School of Medicine, New Haven,
CT 06536-0812.
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