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Molecular and Cellular Biology, March 1999, p. 2380-2388, Vol. 19, No. 3
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Analysis of a Ubiquitous Promoter Element in a Primitive Eukaryote: Early Evolution of the Initiator Element

David R. Liston and Patricia J. Johnson*

Department of Microbiology and Immunology and Molecular Biology Institute, University of California, Los Angeles, School of Medicine, Los Angeles, California 90095-1489

Received 10 September 1998/Returned for modification 11 November 1998/Accepted 28 November 1998

Typical metazoan core promoter elements, such as TATA boxes and Inr motifs, have yet to be identified in early-evolving eukaryotes, underscoring the extensive divergence of these organisms. Towards the identification of core promoters in protists, we have studied transcription of protein-encoding genes in one of the earliest-diverging lineages of Eukaryota, that represented by the parasitic protist Trichomonas vaginalis. A highly conserved element, comprised of a motif similar to a metazoan initiator (Inr) element, surrounds the start site of transcription in all examined T. vaginalis genes. In contrast, a metazoan-like TATA element appears to be absent in trichomonad promoters. We demonstrate that the conserved motif found in T. vaginalis protein-encoding genes is an Inr promoter element. This trichomonad Inr is essential for transcription, responsible for accurate start site selection, and interchangeable between genes, demonstrating its role as a core promoter element. The sequence requirements of the trichomonad Inr are similar to metazoan Inrs and can be replaced by a mammalian Inr. These studies show that the Inr is a ubiquitous, core promoter element for protein-encoding genes in an early-evolving eukaryote. Functional and structural similarities between this protist Inr and the metazoan Inr strongly indicate that the Inr promoter element evolved early in eukaryotic evolution.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of California, Los Angeles School of Medicine, 1602 Molecular Sciences Building, 405 Hilgard Ave., Los Angeles, CA 90095-1489. Phone: (310) 825-4870. Fax: (310) 206-5231. E-mail: johnsonp{at}ucla.edu.

Molecular and Cellular Biology, March 1999, p. 2380-2388, Vol. 19, No. 3
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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J. Bacteriol. J. Virol. Eukaryot. Cell
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Copyright © 1999 by the American Society for Microbiology. All rights reserved.