Regulation of Gene Expression

Gene activity is not the same all the time. Under some conditions the rate of expression may be very high, sometimes gene can be switched off so that reaction to the environmental changes is possible. Cells have different functions and structure what also results from selective expression and repression of genes. There are certain mechanisms that regulates this changes.

Gene expression can be regulated on different stages and in many possible ways. The process is not fully understood and there is more information about prokaryotic cells rather than eukaryotic

Chromatin structure
Densely packed chromatin (heterochromatin) prevent DNA from contact with enzymes such as polymerase and thus expression is impossible in those regions. Proteins involved in transcription can start their work only in euchromatin.

Gene Structure
Promotor regions are proceeded by specific sequences that influence efficiency of attaching polymerase to DNA chain. The speed of transcription’s initiation is regulated by the number of repeats of special elements called UPE. The speed of transcription itself is regulated by enhancing sequences which can affect gene expression even when placed far from the gene promotor. Enhancers can activate speeding up the transcription only in some types of cells.

Regulating Proteins
Proteins usually attach to the DNA chain in the region of promotor and enhancers. For example attachment of certain proteins in so called TATA region before the promotor determines whether polymerase can initiate transcription or not. Those proteins increase polymerase’s affinity to that region of DNA. It is assumed that modulating sites in DNA are placed in such a way that they make a loop. Consequently proteins are in close nearby of the transcribing enzymes and influence the process. Proteins can act as enhancers as well as repressors.

pre-mRNA treatment
Some genes contain more than one signal for adding the poli-A sequence thus from the same pre-mRNA different functional RNA can be formed. Also sometimes exons are treated like introns and cut out. The same gene can be a matrix for synthesis of different proteins in different types of cells.