Everything about RNA — Part 2

RNA, Everything about it.

Introduction
Synthesis of an mRNA molecule Part 1
Synthesis of an mRNA molecule Part 2
Termination of mRNA synthesis

The synthesis of a single strand of mRNA

DNA systhesis and replication can always start and proceed at any given locus, but doing the same for RNA would be wasteful. Certain proteins need to be synthesized at certain periods of the life cycle of the cell and certain others degraded. Specificity is required in transcription. The information for the initiation of the transcription is found on the DNA itself. Certain specific conserved regions termed promoters sit a few base pairs upstream the gene to be transcribed and act as binding sites for the RNA polymerase to bind and begin transcription.

The different promoters of several bacterial genes have certain nucleotides in common, the so-called consensus sequences. The promoter region for any gene seems to begin at the -10 base (from the first base of the gene to be transcribed) and continue thencewards. The -10 and the -35 regions in the promoter contains the consesus sequences. The most common consesus sequence in the -10 region is the Prinbow box with the sequence (5')TATAAT(3') and
(5')TTGACA(3') in the -35 region.

Two steps are discerned in the initiation of transcription by promoters
>The sigma factor of the RNA polymerase binds to the other subunits and attaches the enzyme to the -35 region of the DNA. This results in the formation of the closed-complex.
>The whole enzyme complex migrates to the -10 region and the DNA strands are sepetated leading to the formation of the transcription bubble. This is the open complex (referring to the state of the double stranded DNA helix in the enzyme-DNA complex).

mRNA polymerization starts and the sigma factor subssequently dissosciates from the enzyme complex.