Gene Regulation

Sigma Factor

  • transcription factor

  • recognizes the promoter and brings RNA polymerase to that point to start transcription

  • Sigma factor brings rna polymerase to promoter and then the strands melt apart and separate because rna polymerase only copies one of them.

  • Promoter: recognition for sigma factor or transcription factor

  • +1 notes the start of transcription

  • -10 is the meltpoint

  • RNA: 5’-3’

  • One gene: One protein

  • Ribosome binding site: region of RNA where ribosome recognizes it should start

Transcriptional Regulation

  • Inducer: Binds to repressor makes it let go and start transcription

  • Target gene is expressed only when the inducer is present, or the corepressor or repressor protein are not

  • In the absence of lactose, there is a repressor protein called lacI that’s under its own promoter that will bind to regions shown in green called lacO and lacOI that basically shuts off transcription of the operon.

  • Lactose operon is three genes (LacZYA)

    • LacZ: breaks down lactose

    • LacY: how lactose gets into the cell (lactose transporters)

    • LacA: not really known

  • LacZYA is shut off by the Laci repressor binding to the two regions and looping the DNA out preventing physical access to the promoter

  • LacI will form a tetramer and block access

  • When lactose becomes available, it can be brought in because there are a few transporters. At low levels, LacZ doesn’t break down lactose immediately. It will isomerize it. Instead of it breaking lactose down to galactose and glucose, it rearranges lactose into allolactose

  • Allolactose is the inducer that binds to LacI repressor and cause it to let go.

  • Chromatin in closed conformation: transcription is inactive

  • Promoters that have methylated residues are transcriptionally inactive

Translational

RNA Interference (RNAi)

  • bind to mRNA transcripts and prevent translation

  • siRNA or miRNA complexes with RSC complex. This complex will find the target mRNA. If the 20 base sequence of miRNA or siRNA is fully complementary to part of its target mRNA, this will be recognized in the protein of the RSC complex will cut the RNA and cause it to degrade.

  • if 7 out of 20 bases, then translation would just pause because the mRNA isn’t degraded.

  • 3’ untranslated region- binding site for miRNA/siRNA

Adult hemoglobin is alpha and beta

Fetal hemoglobin is alpha and gamma

sickle cell anemia affects the beta gene

Focus: Discuss different levels of regulation, transcription is most common, lactose operon, translational reg RNAi, explain activators and repressors, and chromatin structures

post-translation: clotting cascade (anything that happens to a protein after it’s been synthesized)/ phosphorylated and activated (insulin has to be cleaved to be activated)