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【多选题】
How do transcription regulators, general transcription factors, and RNA polymerase gain access to the underlying DNA in highly packed chromosomes?A.
In eukaryotic cells, activator and repressor proteins can exploit the mechanisms used to package DNA to help turn genes on and of.
B.
Chromatin structure can be altered by chromatin-remodeling complexes and by enzymes that covalently modify the histone proteins that form the core of the nucleosome. Many gene activators take advantage of these mechanisms by attracting such chromatin-modifying proteins to promoters.
C.
For example, the recruitment of histone acetyltransferases promotes the attachment of acetyl groups to selected lysines in the tail of histone proteins; these acetyl groups themselves attract proteins that promote transcription, including some of the general transcription factors. And the recruitment of chromatin-remodeling complexes makes nearby DNA more accessible. These actions enhance the efficiency of transcription initiation.
D.
In a similar way, gene repressor proteins can modify chromatin in ways that reduce the efficiency of transcription initiation. For example, many repressors attract histone deacetylases—enzymes that remove the acetyl groups from histone tails, thereby reversing the positive effects that acetylation has on transcription initiation.
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举一反三
【多选题】在终身学习的时代,学习关于教育和学习的规律,________。
A.
是职业教师的事，与大众无关
B.
为效开展终身学习，有必要了解并在此指导下行动
C.
大学生将相关理论与自己学习的感受联系起来，这件事情是有价值的
D.
非教育行业的人士没有必要知道。
【单选题】—_____ your brother like hamburgers? —No, he _____. [ ]
A.
Do; doesn't
B.
Do; don't
C.
Does; doesn't
【单选题】— Simon playing computer games? —No, he . [ ]
A.
Do; like; don't
B.
Do; likes; doesn't
C.
Does; like; doesn't
D.
Does; likes; doesn't
【单选题】.My father_____like______basketball.
A.
do;playing
B.
doesn’t;play
C.
does;play
D.
doesn’t;playing
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