Topic 15, Regulation of gene expression in eukaryotes

  1. Eukaryotic genomes are very different from prokaryotic genomes because:
    A. They are much larger
    B. There are many chromosomes rather than just one
    C. A nuclear membrane separates transcription from translation
    D. The transcripts are processed before transport to the cytoplasm
    E. Eukaryotic mRNA has a much longer half-life than prokaryotic mRNA
    F. Nucleosomes are present in eukaryotic DNA

  2. Promoters and enhancers are involved in regulation of transcription
    A. Promoters     = recognition point for RNA polymerase binding.
        1. Necessary to initiate transcription
        2. Are located a fixed distance upstream from the gene to be transcribed
        3. Are several hundred nucleotides in length.
        4. Are considered to be part of the gene
        5. Components:
            a, TATA box, 25-30 bases upstream
            b. CAAT box often present, 70-80 bases upstream
            c.GC box, ~110 basses upstream, may be present in multiple copies
    B. Enhancers     control chromatin structure and the rate of transcription
        1. Cis-acting
        2. Can increase transcription rates
        3. Can be on either side of the gene or even within the gene
        4. Can act at long distances, up to 50 kb in some cases
        5. Typically interact with multiple regulatory proteins and can increase the efficiency of transcription
        6. Can be tissue-specific
        7. Can even be in reverse orientation
        8. Are analogous in some ways to an operator

  3. Trans-acting factors
    A. Large number
    B. Some bind to the enhancer region and others to promoter
    C. Many have two domains,
        1. One binds to DNA and
        2. The 2nd binds to RNA polymerase or another transcription factor at the promoter
    D.     Motifs found in transcription factors (not discussed in lecture, you are not responsible for these)
        1. Helix-turn-helix
        2. Homeobox
        3. Zinc finger
        4, Leucine zipper

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    Updated 12/3/99