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Study Questions Lectures 14/15 – Transcription and chromatin structure Question 1 For each of the following circle the “T” if the statement is true and the “F” if the statement is false. T F Changes in chromatin structure that result in changes in gene expression can be associated with covalent modification of both histone proteins and the DNA itself. Histone acetylation/methylation, DNA methylation T F Southern blot analysis of specific genes after micrococcal nuclease treatment showed that genes that are transcribed in a specific tissue are completely free of nucleosomes. The opposite result was observed. Genes that are transcribed are still packaged into nucleosomes (the nucleosomes are transiently removed as the polymerase passes then reassembled. ..the array is dynamic rather than static). T F Methylation of DNA in promoter regions facilitates the recruitment of histone deacetylases to these same regions. DNA binding proteins that recognize me-C, such as MeCP2, can be responsible for this. T F Nucleosome remodeling complexes are used to pack nucleosomes into less accessible chromatin structures that make it more difficult to express genes Remodeling complexes such as SWI/SNF use ATP energy to move nucleosomes, which can reveal hidden binding sites for transcription factors. T F Bromo domain- containing proteins recognize modifications, such as methylation on specific histone residues, which are associated with chromatin silencing. Chromo domain proteins would do this T F Binding of a “pioneer” transcription factor to an enhancer before packaging of DNA in that area into nucleosomes can result in specific positioning of nucleosomes in the surrounding chromatin to leave a “nucleosome free region”. Initial binding of a key transcription factor can restrict incorporation of that region into nucleosomes and make it easier for other transcription factors to bind to that region later to activate gene expression. Question 2. You have fractionated nuclear extracts from sea urchins. A specific set of these fractions can be combined into a "transcription mix" that is sufficient to promote active transcription of genes in purified chromatin from which histone H1 has been removed. Subsequent experiments showed that adding back histone H1 to the chromatin prior to adding the transcription mix led to a 25-fold lower level of transcription. In contrast, if the transcription mix was added first, subsequent addition of histone H1 had little or no effect on transcription. Circle "T" or "F" to indicate whether each of the statements below is true or false, respectively. Use both the information above, and your knowledge from the course lecture and readings to answer the questions.
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T F Factors in the transcription mix appear to interfere with histone H1 interaction with the transcribed genes. Inhibition by H1 is blocked by transcription factors so interaction must be at least partially blocked T F In the above experiments, gene transcription is inhibited by the
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This note was uploaded on 02/26/2012 for the course MCB 121 taught by Professor Gasser during the Winter '09 term at UC Davis.

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