Novel critical role of a human Mediator complex for basal RNA polymerase II transcription

Authors

  • Gerhard Mittler,

    1. Institute of Molecular Immunology, Department for Gene Expression, GSF-National Research Center for Environment and Health, München, Germany
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  • Elisabeth Kremmer,

    1. Institute of Molecular Immunology, Department for Gene Expression, GSF-National Research Center for Environment and Health, München, Germany
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  • H Th. Marc Timmers,

    1. Laboratory for Physiological Chemistry, University Medical Center Utrecht, Universiteitsweg 100, Utrecht, The Netherlands
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  • Michael Meisterernst

    Corresponding author
    1. Institute of Molecular Immunology, Department for Gene Expression, GSF-National Research Center for Environment and Health, München, Germany
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Abstract

Human Mediator complexes have been described as important bridging factors that enhance the effect of activators in purified systems and in chromatin. Here we report a novel basal function of a human Mediator complex. A monoclonal antibody was generated that depleted the majority of Mediator components from crude cell extracts. The removal of human Mediator abolished transcription by RNA polymerase II. This was observed on all genes tested, on TATA-containing and TATA-less promoters, both in the presence and absence of activators. To identify the relevant complex a combined biochemical and immunopurification protocol was applied. Two variants termed Mediator and basal Mediator were functionally and structurally distinguished. Basal Mediator function relies on additional constraints, which is reflected in the observation that it is essential in crude but not in purified systems. We conclude that basal Mediator is a novel general transcription factor of RNA polymerase II.

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