4. RNA synthesis occurs in a moving transcription bubble on the DNA template o Only a short RNA-Dna hybrid(8 bp in bacteria) is present through the transcription process At each moment, a region of about l7 bp on the e coli dna is unwound in the transcription bubble The rna chain is extended at a rate of 50-90 nucleotides/ second by the E coli rna polymerase o Unwinding ahead of and rewinding behind of the transcription bubble produces positive and negative supercoils respectively on the dna (relieved by the action of topoisomerases)4. RNA synthesis occurs in a “moving” transcription bubble on the DNA template ⚫ Only a short RNA-DNA hybrid (~8 bp in bacteria) is present through the transcription process. ⚫ At each moment, a region of about 17 bp on the E. coli DNA is unwound in the transcription bubble. ⚫ The RNA chain is extended at a rate of 50-90 nucleotides/second by the E. coli RNA polymerase. ⚫ Unwinding ahead of and rewinding behind of the transcription bubble produces positive and negative supercoils respectively on the DNA (relieved by the action of topoisomerases)