Initiator recognition in a primitive eukaryote: IBP39, an initiator-binding protein from Trichomonas vaginalis.
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.
Liston
D R
DR
Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles School of Medicine, Los Angeles, California 90095-1489, USA.
Lau
A O
AO
Ortiz
D
D
Smale
S T
ST
Johnson
P J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002846:Chromatography, Affinity / Q000379:methods; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D005057:Eukaryotic Cells; D008969:Molecular Sequence Data; D015800:Protozoan Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D024363:Transcription Initiation Site; D014246:Trichomonas vaginalis / Q000235:genetics* / Q000378:metabolism*
D016054:DNA, Protozoan; D004268:DNA-Binding Proteins; C438871:IBP39 protein, Trichomonas vaginalis; D015800:Protozoan Proteins