Transcription bubble Nontemplate 大肠杆 strand RNA polymerase 菌中的 Rewinding 5 Unwinding RNA聚 DNA 酶转 Template strand 录RNA RNA RNA-DNA Active site hybrid. 8 b Direction of transcription Negative supercoils Positive supercoils 5 RNA Direction of transcription (b)大肠杆 菌中的 RNA聚 合酶转 录RNA