Class Notes (838,050)
Canada (510,626)
Biochemistry (847)
Lecture

Regulation of Gene Expression

3 Pages
57 Views
Unlock Document

Department
Biochemistry
Course
Biochemistry 2280A
Professor
Derek Mc Lachlin
Semester
Fall

Description
Brandl Lecture 2 Notes: REGULATION OF GENE EXPRESSION 11/09/2012 Methods of Regulation 1. Some genes have better -10 and -35 sequences  These genes will be expressed at higher levels  W ill recruit RNA polymerase at higher efficiency  Not dynamic  Sequences cannot be regulated; are “stuck” with that sequences throughout time 2. There is more than one sigma factor  Each recognizes different promoters  The most prevalent is the “housekeeping” σ, σ70 54 HS  Others include σ nitrogen metabolism, σ heat shock  Heat shock responds to high temperature, is induced and reacts with RNA core enzyme 3. Gene specific regulatory proteins  Dynamic!  Can change genes in response to different environmental signals through these gene specific regulatory proteins  Largely used by eukaryotic cells  Negative regulation – factors repress transcription  Positive regulation – factors activate transcription Negative Regulation Example: trp operon  In E. coli the 5 genes for tryptophan biosynthesis are transcribed from a common promoter  The trp operon is regulated by the concentration of tryptophan in the environment  Trp operon is expressed when there is little tryptophan in the cellular environment  How is the trp operon regulated by tryptophan? Trp Promoter  σ regulated promoter  Between the -10 and -35 sequences is an element called the trp operator that binds a protein called the trp repressor  At high [tryptophan], trp repressor binds tryptophan  The trp repressor-tryptophan complex binds the operator DNA  The trp-repressor-tryptophan complex blocks RNA polymerase from the promoter  RNA polymerase cannot bind to the promoter; it is sterically inhibited from getting there  Polymerase can’t park at the promoter  When [tryptophan] is low, tryptophan dissociates from the trp repressor  The trp repressor no longer binds the trp operator  The trp repressor will only bind DNA when it itself is bound to tryptophan Result  RNA polymerase can access the trp operator, transcription occurs  Low [tryptophan] – genes are on  High [tryptophan] – genes are off  What is the structural basis for the regulation by tryptophan? Trp Repressor – Monomer  107 amino acid residues  Alpha helices 4 and 5 make up the helix-turn-helix motif  Helices 4 and 5 are critical  Helix-turn-helix motif is crucial for binding DNA  Many DNA-binding proteins act as dimers  Can be true dimers like (trp repressor) or pseudo-dimers Trp Repressor – Dimer  Protein dimer has 2-fold symmetry  Helix 3s contact to allow dimerization  Helix 5 of each monomer recognizes adjacent major grooves in the operator DNA  Major groove is wide enough to fit an alpha helix  Protein can read the bases in the major groove  Most proteins interact with major groove, not minor groove  Minor groove is too small, doesn’t have much discriminatory power  Repressor only binds to DNA when it has tryptophan bound to it  Tryptophan binding induces a conformational change in the Trp repressor which allows DNA binding  Binding of tryptophan is crucial to remaining conformation of protein that will bind to DNA  Tryptophan binds to protein, alters conformation of protein (from tilted helix 5s to new conformation)  Process has been selected for through evolution General Themes to take from the Trp Operon 1. Trp repressor is a site specific DNA binding protein  Binding to specific sequences very tightly  Recognize individual specific sequences 2. There is a binding site for trp repressor within the Trp promoter  Genes that don’t have an operator won’t be regulated by the trp repressor; binding site is needed 3. Trp repressor inhibits transcription by blocking access of RNAP to the promoter 4. Trp repressor is responsive to an environmental signal  For Trp repressor, this would be tryptophan (environmental signal)  All gene specific regulatory proteins are regulated by some signal  Q: Genetics has been critical in understanding the regulation of the trp operon. Dif
More Less

Related notes for Biochemistry 2280A

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit