ABSTRACT
Transcription by E. coli RNA polymerase occurs in three phases; initiation, elongation and termination. Initiation involves binding of the enzyme to a promoter upstream of the gene. During elongation, the antisense DNA strand is used as the template so that the RNA made has the same base sequence as the sense strand, except that uracil replaces thymine. A termination signal is eventually encountered that halts synthesis and causes release of the completed RNA. Transcription continues until a termination sequence is reached. The most common termination signal is a guanine-cytosine-rich region that is a palindrome, followed by an adenine-thymine-rich sequence. In prokaryotes, RNA transcribed from protein-coding genes, requires little or no modification prior to translation. In fact, many messenger RNA molecules begin to be translated even before RNA synthesis has finished. However, ribosomal RNA and transfer RNA are synthesized as precursor molecules that do require post-transcriptional processing.
