13BIS101S2013GeneRegulLect13-1

Lrodriguez 18 lactose repressor when the inducer

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: repressor acts as a homotetramer (four identical subuntis. Lac Functional repressor has two (2) principal domains: the DNA domain at the N-terminus that binds the operator (circles); and the C-terminal domain that binds the inducer lactose. the operator binding site inducer binding binding site site BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 18 Lactose Repressor When the inducer, (lactose, allolactose or IPTG) is bound in the When inducer binding site, it induces an allosteric conformational change in the DNA binding site that prevents binding of the repressor to the operator. operator binding closed bound bound inducer Lactose BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 19 Merodiploid Complementation 2 In this merodiploid, the I+ gene makes functional repressor. However, In because the operator has mutated (Oc), the repressor can only bind to O+ because ), not Oc. In this case, the operator mutant (Oc) iis cis-dominant to (O+) and s cis-dominant and the I+ gene. The phenotype of this merodiploid is constitutive. constitutive I+ P+ O+ Z+ I+ P+ Oc Z+ = constitutive expression of β-gal constitutive BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 20 Lac Operator Mutation Movie BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 21 Merodiploid Complementation 3 In the merodiploid shown below, the Is gene makes a repressor with a In binding site for the operator DNA sequence but no binding site for the inducer. In this case, the Is binds to the operator and cannot be induced off with lactose or IPTG. This mutant repressor is call the super repressor and it is trans-dominant to I+. repressor trans-dominant Is P+ O+ Z+ I P O Z + + + + = β-gal unducible BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 22 Superrepressor Mutation Movie BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 23 Operator Nucleotide Sequence -10 -10 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 24 Lac Repressor Binding Operator DNA -35 2 operator binding sites separated by a 93 bp loop 93 CAP binding at -60 -10 4 2 Repressor tetramer 3 1 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 25 Operon Model: Negative Control What about positive control? BIS101­001, Spring 2013—Genes and G...
View Full Document

This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

Ask a homework question - tutors are online