Regulatory Sequences and Molecules

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Chapter: Biochemistry : Regulation of Gene Expression

Regulation of transcription, the initial step in all gene expression, is controlled by regulatory sequences of DNA, usually embedded in the noncoding regions of the genome.


REGULATORY SEQUENCES AND MOLECULES

Regulation of transcription, the initial step in all gene expression, is controlled by regulatory sequences of DNA, usually embedded in the noncoding regions of the genome. The interaction between these DNA segments and regulatory molecules, such as transcription factors, can engage or repress the transcriptional machinery, influencing the kinds and amounts of products that are produced. These DNA sequences flanking a gene are called cis-acting because they influence expression of genes only on the same chromosome. A trans-acting factor is the regulatory molecule itself, which can transit (diffuse) through the cell from its site of synthesis to its DNA-binding site (Figure 32.2). For example, a protein transcription factor (a trans-acting molecule) that regulates a gene on chromosome 6 might itself have been produced from a gene on chromosome 11. The binding of proteins to DNA is through structural motifs such as the zinc finger (Figure 32.3), leucine zipper, or helix-turn-helix in the protein. [Note: Some trans-acting factors can negatively affect gene expression.]


Figure 32.2 Cis-acting elements and trans-acting molecules. mRNA = messenger RNA; Pol II = RNA polymerase II.


Figure 32.3 Zinc (Zn) finger is a common motif in proteins that bind DNA. Cys = cysteine; His = histidine.

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