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A position effect in the control of transcription at yeast mating type loci

K A Nasmyth, K Tatchell, B D Hall

    Nature
    |January 22, 1981
    PubMed

    Insights

    Silent mating type loci (HMRa and HML alpha) in yeast do not transcribe despite identical DNA sequences. This suggests regulatory sequences located far away influence gene expression.

    Area of Science:

    • Molecular Biology
    • Yeast Genetics

    Background:

    • Mating type loci (MATa and MAT alpha) in yeast are crucial for sexual reproduction.
    • These loci produce specific mRNAs transcribed from central promoters.
    • Silent copies, HMRa and HML alpha, share identical DNA sequences with expressed loci but are not transcribed.

    Purpose of the Study:

    • To investigate the mechanism behind the transcriptional silencing of HMRa and HML alpha loci.
    • To understand how distant DNA sequences regulate transcription initiation.

    Main Methods:

    • Comparative analysis of DNA sequences between expressed and silent mating type loci.
    • Investigating the role of flanking sequences in transcriptional regulation.

    Main Results:

    • Identical transcribed regions in silent loci (HMRa, HML alpha) do not correlate with gene expression.
    • Transcription is repressed in silent loci despite promoter presence.
    • Evidence suggests regulatory sequences located proximally to the left of HMRa (and likely HML alpha) are responsible for silencing.

    Conclusions:

    • Transcriptional silencing of mating type loci is regulated by position effects.
    • Distant DNA sequences, located 700-1,400 base pairs upstream, play a critical role in repressing transcription initiation at HMRa and HML alpha.
    • A potential mechanism for this long-range position effect is proposed.

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