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1. eukaryotic

1.1. types of polymerases

1.1.1. RNA polymerase I located in the nucleolus catalyzes the synthesis of 28S, 18S, and 5.8S rRNA molecules

1.1.2. RNA polymerase II located in the nucleoplasm synthesizes messenger RNAs and some small nuclear RNAs

1.1.3. RNA polymerase III located in the nucleoplasm synthesizes tRNAs, 5S rRNA, a small rRNA molecule found in each ribosome, and the snRNAs

2. Prokaryotic

2.1. steps

2.1.1. Initiation Promoter A sequence of DNA upstream of a gene which is to be encoded where RNA Polymerase binds to initiate Transcription. Ensures initiation of transcription at the same site. RNA chain synthesized in 3'-to-5' direction, with only one strand of the DNA as a template. No primer is required in the process. DNA sequences critical for specifying the initiation of transcription (the -35 box) 5’-TTGACA-3’. (the -10) 5’-TATAAT-3’. One type of RNA polymerase holoenzyme sigma factor Process: The holoenzyme contacts the -35 sequence.

2.1.2. Elongation The RNA polymerase begins to move along the DNA The sigma factor is released Process: RNA polymerase becomes more compact, contacting less of the DNA.

2.1.3. Termination The termination of bacterial gene transcription is signaled by terminator sequences Process: The RNA polymerase transcribes the terminator sequence which is part of the initial RNA coding sequence of the gene the inverted repeat arrangement makes the RNA fold into a hairpin loop structure string of U nucleotides downstream of the hairpin destabilizes the pairing between the new RNA chain and the DNA template strand causing RNA polymerase to dissociate from template strand

3. Rho-independent terminators.

3.1. consist of an inverted repeat sequence that is about 16 to 20 base pairs upstream of the transcription termination point

3.2. followed by a string of about 4 to 8 A–T base pairs.

4. Rho-dependent terminators

4.1. the protein Rho (ρ) plays a role in the termination of transcription of some genes

4.2. They are C-rich, G-poor sequences that have no hairpin structures like those of rhoindependent terminators.

4.3. Rho binds to the C-rich terminator sequence in the transcript upstream of the transcription termination site

4.4. Rho then moves along the transcript until it reaches the RNA polymerase, where the most recently synthesized RNA is base paired with the template DNA.