Ch. 14/15: Control of Gene Regulation

repressor protein

• What the lac operon is regulated by

operon

• multiple genes controlled by 1 promoter

lacZ

• codes beta-galactosidase

• enzymatically cleaves lactose and lactose analogs

• also converts lactose to allolactose (an isomer)

lacY

• codes lactose permease

• membrane protein required for transport of lactose and analogues

  • transports lactose into cell

lacA

• codes galactoside transacetylase

lacIgene

• has its own promoter, the i promoter

• codes lac repressor

1st step of induction of the lac operon

• when allolactose is available, it binds to the repressor

2nd step of induction of the lac operon

• the conformation of the repressor protein is altered

• now the repressor can’t bind to the operator site

3rd step of induction of the lac operon

• RNA polymerase transcribes the operon

• Lactose is broken down

ways gene expression is regulated

• transcription

• RNA modification

• translation

• post translation

transcription

• regulatory transcription factors activate or inhibit transcription

RNA modification

• alternative splicing and RNA editing

translation

• Proteins regulate translation or mRNA degradation

• RNA interference

post translation

• feedback inhibition and covalent modifications regulate protein function

activator proteins

• stimulate transcription

repressor proteins

• inhibit transcription

activators and repressors

• may be modulated by binding of small effector molecules, protein-protein interactions and covalent modifications

regulatory proteins

• may alter nucleosomes near the promoter

DNA methylation

• may inhibit transcription

regulatory transcription factors

• recognize cis regulatory elements within enhancers

• when they bind to regulatory elements they affect the transcription of an associated gene

  • they can be activators or repressors

nucleosome

• repeating structural unit within eukaryotic chromatin

• it is composed of a double-stranded segment of DNA wrapped around an octamer of histone proteins

histone octamer

• is composed of two copies each of four different histone proteins

histone proteins

• are basic

• the contain many positive-charged amino acids

  • lysine and arginine

• these bind to the negatively-charged phosphates along the DNA backbone

• have a globular domain and a flexible, charged amino acid tail

ATP dependent chromatin remodeling

• change in nucleosome position

• histone eviction

• replacement with histone variants

Histone acetylation

• histone acetyltransferases (HATs) modify positively charged lysines within core histone proteins

• Attachment of the acetyl group disrupts the electrostatic attraction between the histone protein and the negatively charged DNA backbone

• favors open conformation

histone deacetylation

• favors a tighter contact between histones and the DNA

• histone deacetylases remove acetyl groups from acetylated histones

DNA methylation

• inhibits gene transcription

• the covalent attachment of methyl groups

• carried out by DNA methyltransferase

CpG Islands

• found near promoters of genes in vertebrates and plants

• they contain a high number of CpG sites

housekeeping genes

• CpG islands are unmethylated

• genes tend to be expressed in most cell types

tissue specific genes

• The expression of these genes may be silenced by the methylation of CpG islands

• methylation may influence the binding of transcription factors

• Methyl-CpG-binding proteins may recruit factors that lead to compactation of the chromatin

de novo methylation

• mechanism for how specific genes are methylated in gametes from female or male parents

maintenance methylation

• mechanism for how the pattern of one copy of the gene being methylated and the other not is maintained in the resulting offspring