Regulation is the controlled expression of gene functions. This can be done in many ways, but these can be grouped into two classes. The level of enzyme activity can be regulated by noncovalent or covalent modification of a protein. The amount of the protein can also be regulated. This latter class of regulation can be exerted at any step in the pathway of gene expression or during protein turnover. For many (perhaps most) genes, the principal level of regulation of expression is at transcription, and Part Four of this course will focus primarily on this. However, post-transcriptional control is also important in many genes, and this will also be discussed.
- 15: Positive and negative control of gene expression
- An operon is a cluster of coordinately regulated genes. It includes structural genes(generally encoding enzymes), regulatory genes(encoding, e.g. activators or repressors) and regulatory sites(such as promoters and operators).
- 18: Transcriptional regulation after initiation
- Although regulation of the initiation of transcription appears to be a dominant factor in control of expression of many genes, the importance of regulation after initiation is becoming better appreciated in an increasing number and variety of systems.
- 19: Transcriptional regulation in eukaryotes
- Various active genes can be transcribed at distinctive rates, primarily determined by the differences in rate of initiation. This ultimately produces the characteristic abundance of each mRNA, ranging from very high to very low.
- 20: Transcriptional regulation via chromatin alterations
- Chromatin, not naked DNA, is the substrate for transcription, replication, recombination, repair and condensation during mitosis and meiosis. Thus the extent of compaction of the chromatin in the different states will affect the ability of transcription factors, polymerases, repair enzymes, and the recombination machinery to access this substrate. More open, accessible chromatin is associated with greater transcriptional activity.