Lecture 16: Gene Regulation in Eukaryotes

I. Similarities and differences in Gene Regulation between Prokaryotes and Eukaryotes

TABLE 17.1

II. Genetic Studies of Gene Regulation

Mutations that effect gene function but not amino acid content of gene product

Cis-acting regulatory mutations map near the target gene

attachment sites for DNA-binding proteins

promoter- binds RNA polymerase

enhancers- bind proteins that increase or decrease base levels of transcription, can be far from gene

identify using reporter constructs

Trans-acting regulatory mutations map far from target gene

encode proteins or RNAs that interact with target genes cis-acting elements, aka transcription factors

identify by experiments which detect binding to DNA

III. How regulatory elements act

Most gene regulation occurs at the initiation of transcription

A. First evidence:

3 different types of RNA polymerases

•responsible for transcription of rRNA

•responsible for transcription for all protein

encoding genes

•responsible for transcription of tRNAs

•

B. Cis-acting regions

recognized by pol II

consist of a promoter and 1 or more enhancers

promoter close to gene- initiation site and TATA box

TATA box:

TATA (A or T) A (A or T)

located about 30 nucleotides upstream of initiation site

enhancers can be 1000’s nucleotides upstream

C. Trans-acting proteins control transcription from class II promoters

Basal factors bind to promoter Activators and repressors bind to enhancers

TATA Box- binding protein(TBP)- Key Component of Basal Factor Complex

TBP essential for initiation of transcription of all class

II genes (proteins) having a TATA box in promoter

TBP + TAF (TBP associated factors) = then transcription

highly conserved in eukaryotes

Promoters and Enhancers- assist binding of RNA polymerase II to promoter.

Activator- binds to specific enhancer DNA

interacts in/directly with basal factors

increase transcription initiation

2 important domains allow activator proteins to bind to DNA and to other proteins to activate transcription

different aa sequence allows specificity to DNA

some activators have a domain which responds to environmental cues

How are the domains localized by geneticists (

Fig 17.6)

D. Repressors

transcription factors that suppress activation of

transcription by activator proteins

operate by:

competition with activator proteins for binding site

bind directly to an activator = quenching

bind to DNA sequences close to promoter

IV. Globin locus control, an example

V. Chromatin and gene regulation

Chromatin consists of histone protein that compact DNA, making it inaccessible to polymerase

VI. Regulation after transcription

A. Differential RNA splicing

Sx1 protein blocks exon 3 and mRNA is productive

B. Control by mRNA stabilization

C. mRNA editing

Sequence difference between genomic DNA and mRNA, occurs after transcription and splicing, can synthesize different acting proteins from same sequence

VII. Conclusion

Many different ways of gene regulation

Molecular biologists have spent the last 30 years trying to quantify all the ways genes are regulated

Knowledge of the genome sequence does not tell us much if we do not know how genes are turned on and off

Terms and Concepts to know:

cis and trans acting elements, transcription factors, basal factors, activators, repressors, TATA box,

promoter, enhancer, TBP, TAF, Gal gene system, role of chromatin, Regulation after transcription,

RNA splicing, RNA stability, mRNA editing

Figs and Tables: T 1, Figs 1, 4, 5, 6, 8, 11, 13, 16, 17, 18