CAP是lac operon的positive regulatio，因为
A).CAP binds cAMP
B).CAP binds the CAP binding site
C).CAP prevents binding of the repressive to the operator
D).CAP bound to the CAP binding site increase the frequency of transcription i
nitiation by RNA pol
有关promoter clearance of transcription initiation 正确的？
A).RNA pol unwinds the DNA at the start site of transcription
B).RNA pol pauses before joining the first two nucleotide of the mRNA
C).a small RNA has been synthesized and some domains of sigma factor dissociat
e from RNA pol
D).activator and repressive dissociate from the promoter and sigma factor full
y dissociate from RNA
没有arabinose，the regulatory protein Arac会？
A).form a dimer,binds to two regulatory sequence near the promoter,and activat
es transcription of the arabinose oberon structural genes
B).form a dimer,binds to two distant sites,and forms a DNA loop that blocks ac
cess of RNA pol to the arabinose operon promoter
C).binds to the arabinose operator and repress transcription of the arabinose
operon structural genes
在写来路不明的考题时，跟同学讨论不出个所以然，希望有高手可以分享一下自己的答案
QQ 先谢谢大家的帮忙