Question

Describe in detail the structure of the RNA polymerase II CDT and how the structure is used to sequentially regulate the maturation of the pre-mRNA during the elongation phase of transcription. Focus on the events which happen on RNA polymerase II CDT. For mechanisms which are directly responsible for pre-mRNA processing, you only need to mention their names.

Answer 1

RNA POLYMERASE || :

A RNA polymerase (RNAP), or ribonucleic acid polymerase, is a multi subunit enzyme that catalyzes the process of transcription where an RNA polymer is synthesized from a DNA template. The sequence of the RNA polymer is complementary to that of the template DNA and is synthesized in a 5’→ 3′ orientation. This RNA strand is called the primary transcript and needs to be processed before it can be functional inside the cell.

RNA polymerases interact with many proteins in order to accomplish their task. These proteins help in enhancing the binding specificity of the enzyme, aid in unwinding the double helical structure of DNA, modulate the activity of the enzyme based on the requirements of the cell and alter the speed of transcription. Some RNAP molecules can catalyze the formation of a polymer over four thousand bases in length every minute. However, they have a dynamic range of velocities and they can occasionally pause, or even stop at certain sequences in order to maintain fidelity during transcription.

Functions of RNA Polymerase

Traditionally, the central dogma of molecular biology has looked at RNA as a messenger molecule, that exports the information coded into DNA out of the nucleus in order to drive the synthesis of proteins in the cytoplasm: DNA → RNA → Protein. The other well known RNAs are transfer RNA (tRNA) and ribosomal RNA (rRNA) which are also intimately connected with the protein synthetic machinery. However, over the past two decades, it has become increasingly clear that RNA serves a range of functions, of which protein coding is only one part. Some regulate gene expression, others act as enzymes, some are even crucial in the formation of gametes. These are called non-coding or ncRNA.

Since RNAP is involved in the production of molecules that have such a wide range of roles, one of its main functions is to regulate the number and kind of RNA transcripts formed in response to the cell’s requirements. A number of different proteins, transcription factors and signaling molecules interact with the enzyme, especially the carboxy-terminal end of one subunit, to regulate its activity. It is believed that this regulation was crucial for the development of eukaryotic plants and animals, where genetically identical cells show differential gene expression and specialization in multicellular organisms