Protein Expression

There are a number of ways via which protein expression patterns can be moderated:

1.  Transcriptional control

  • Protein expression can be regulated by controlling to amount of transcription (less mRNA = less protein)
  • This level of control is achieved primarily through the coordinated effects of transcription factors and regulatory proteins

2.  RNA processing control

  • This involves regulating the formation of mature mRNA in eukaryotes (e.g. 5’-capping and 3’-polyadenylation)
  • These processes are necessary to help direct the mRNA to the ribosome and prevent its premature degradation

3.  RNA transport control

  • In eukaryotes, RNA must be transported out of the nucleus (through nuclear pores) in order to associate with the ribosome
  • If this transport is prevented, the related protein cannot by synthesised

4.  Translational control

  • Protein expression can also be regulated by controlling the amount of translation
  • This may involve inhibiting ribosomal subunit assembly or actively targeting mRNA for degradation

5.  Protein activity control

  • Protein expression patterns may also be affected by the rate of protein degradation
  • Post-translational modifications (such as ubiquitination or phosphorylation) may target proteins for destruction

Mechanisms of Regulating Protein Expression Levels

protein expression