DNA Transcription The Structure of RNA Polymerase There are two main segments of the RNA polymerase molecule: the core enzyme, and the sigma subunit. These two pieces are together referred to as the "holoenzyme". The core enzyme is itself composed of a beta, beta prime, and two alpha subunits; together the core is responsible for carrying out the polymerization or synthesis of RNA. The sigma subunit of RNA polymerase is the part of the enzyme responsible for recognizing the signal on the DNA strand that tells the polymerase to begin synthesizing RNA. It is through this sigma unit that RNA polymerase is able to initiate transcription. The Start Site and the Promoter Region In prokaryotic cells, free RNA polymerase molecules are constantly colliding with DNA helices. The collision leads to a weak association between the DNA and RNA polymerase, which is soon broken. However, when the RNA polymerase binds to a specific sequence on the DNA, it binds tightly, forming a DNA/RNA polymerase complex. This specific site of binding is called the start
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This note was uploaded on 01/27/2012 for the course BIOLOGY BSC1005 taught by Professor Rodriguez during the Winter '09 term at Broward College.