Ruf 3 - Main Points Lecture 2 Different sigma factors...

Info icon This preview shows pages 1–5. Sign up to view the full content.

Main Points: Lecture 2 Different sigma factors recognize different consensus recognition sites in promoter, allows utilization of different promoters and transcription of different genes under different conditions Constitutive vs. regulated expression: housekeeping genes Repressors and activators Positive vs. negative regulation Concept of a operon: group of coordinately regulated genes, includes a promoter and regulatory sequences such as operator sites and activator binding sites Lac Operon: an example of both + and – regulation of gene expression Negative regulation: E. Coli make a repressor protein (made constitutively) which in the absence of lactose binds to the operator site in the lac operon. Binding of repressor inhibits RNAP. In the presence of lactose, an inducer (allolactose) binds to the repressor and changes the shape of the repressor protein so that it no longer binds well to the operator site. This relieves repression of the promoter.
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Cis vs. Trans In Genetics Cis --- cis mutations affect only the DNA molecule to which they are linked DNA elements can only function in cis Trans --- trans mutations exert their effects through the action of a factor that can diffuse to other sites. Proteins function in trans Effects of a mutant can be determined by adding wild-type copies to the system
Image of page 2
Possible Regulatory Mutants i- : mutant nonfunctional repressor protein I S : super repressor: cannot be inactivated by inducer O C : operator constitutive: cannot be bound by repressor p-: promoter mutant: nonfunctional promoter Cis or Trans?
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

1. Predict the phenotype of a lac I mutant: non-functional repressor a. The lac genes would be expressed efficiently only in the absence of lactose.
Image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern