regulation of gene expression

Positive regulation

When an activator binds to DNA and increases transcription.

Negative regulation

When a repressor binds to DNA and decreases transcription.

Activator

A transcription factor that stimulates transcription when it binds to a regulatory sequence for a gene.

Repressor

A transcription factor that reduces or prevents transcription when it binds to a regulatory sequence for a gene.

lac operon

A group of genes involved in lactose metabolism in prokaryotes.

operator

The region of an operon that acts as the binding site for the repressor.

sigma factors

Proteins that bind to RNA polymerase and direct it to specific classes of prokaryotic promoters.

trp operon

A group of genes involved in tryptophan metabolism in prokaryotes.

mediator

A regulatory protein that interacts with the general transcription factors and RNA polymerase II of the basal transcription apparatus and with specific transcription factors.

silencer

A gene sequence that binds transcription factors and represses transcription.

enhancer

Regulatory DNA sequences that bind transcription factors and either activate or increase the rate of transcription.

general transcription factor

Transcription factors that bind to the promoters of most protein-coding genes and are required for their expression.

specific transcription factor

Transcription factors that have specific regulatory effects only at certain promoters or classes of promoters.

microRNA (miRNA)

Small, noncoding RNA molecules that bind to mRNA to inhibit its translation.

small interfering RNA (siRNA)

Short, double-stranded RNA molecules used in RNA interference.

methylation

The addition of a methyl group (—CH3) to a molecule.

CpG islands

DNA regions rich in C nucleotides adjacent to G nucleotides, where methylation of cytosine usually occurs.

histone deacetylation

The removal of acetyl groups from histone proteins, which increases histone affinity for DNA and reduces transcription.

Xist RNA

RNA produced during X inactivation that coats the chromosome from which it was transcribed, causing it to become heterochromatic.

alternative splicing

A process for generating different mature mRNAs from a single gene by splicing together different sets of exons during RNA processing.