Gene Regulation & Expression

Chromatin Restructuring

• Chromatin is name given to DNA plus histone proteins 

• Transcription can be blocked by histone proteins bound tightly to DNA 

• Epigenetics means a process not dependent on DNA sequences 

• Chromatin restructuring is adjusting how tightly histones are bound to DNA by modification of either the histones or the DNA itself 

• Tighter chromatin (high compaction): little transcription 

• Looser chromatin (little compaction): greater transcription 

Repression

blocking elongation of transcription by the binding of a repressor protein to an operator region downstream of the promotor 

• Repressor is like a brick wall 

• Does not block initiation 

• Blocks elongation of transcription 

• Decreases expression of genes 

• Negative regulation 

Induction

increasing the rate of initiation of transcription by the binding of an inducer molecule near the promotor of a gene 

• Increases the translation of a gene 

• Increases rate of initiation

Increase Gene Expression 

• Relaxed chromatin 

• Induction of transcription (initiation) 

• Stable mRNA 

• Strong ribosomal binding sequence on mRNA 

• Strong splice sites on primary transcript 

• Long-lived protein 

Decrease Gene Expression 

• Tight chromatin 

• Repression of transcription (elongation) 

• Short-lived mRNA 

• Weak ribosomal binding sequence on mRNA 

• Weak splice sites on primary transcript 

• Short-lived protein