ABSTRACT
The Deoxyribonucleic acid (DNA) double helix is unwound for transcription, forming a transcription bubble, and is then rewound after the transcription complex has passed. Messenger ribonucleic acid (RNA) transcripts of protein-coding genes in prokaryotes require little or no modification before translation. Gene transcription by E. coli RNA polymerase takes place in three phases: initiation, elongation and termination. The RNA polymerase encounters a termination signal and ceases transcription, releasing the RNA transcript and dissociating from the DNA. During elongation, the RNA polymerase uses the antisense strand of DNA as a template and synthesizes a complementary RNA molecule using ribonucleoside 5' triphosphates as precursors. Promoters differ by up to 1000-fold in their efficiency of initiation of transcription so that genes with strong promoters are transcribed very frequently whereas genes with weak promoters are transcribed far less often. Transcription continues until a termination sequence is reached.
