{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

5 - TA Christine Feng [email protected] Section Mon 4-5...

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: TA: Christine Feng [email protected] Section: Mon 4-5 Center 205 OH: Wed 11-12 Geisel S&E This Week in Lecture: • Transcription regulation  ­ Cro gene operators • Helix ­turn ­helix motif • Trp repressor • CAP • Zinc Finger Motif • Leucine Zipper Motif • Ch 8, 10 Transcription Regulation • Recall: B ­DNA has distorted helices major & minor groove o Major groove binding is more common – more space for 2 partners to interact • Most genes are silent until turned on: DNA RNA Protein o Controls for growth, differentiation, oncogenesis o Recognition controlled by affinity & specificity • Switch: activator or repressor; usually 2 genes that code for 2 regulator proteins to operate the switch • Genes are transcribed in opposite directions • Operator can be bound by either repressor or Cro (bind as dimers to OR1, OR2, OR3) • Binding of either repressor protein/Cro blocks promoter region of other Helix Turn Helix (HTH) • Unique to DNA ­binding proteins – 2 α helices connected via loop • Form dimers in which recognition α helices are exactly 34Å apart • Corresponds to 1 turn (10 bp) of a B DNA molecule • Sequence specific interactions between helices and DNA • DNA can distort to create close interactions with other regions of protein (fig 8.17) Allosteric Control – trp repressor – midterm question 8 • Allosteric effectors: small ligands that bind to sterically distinct sites (away from functional binding sites) • Trp repressor controls operon that synthesizes L ­trp • 6 α helices that do not form a hydrophobic core • Dimerization results in compact globular form • Absence of trp: helices tilt inward  ­ 29Å distance between binding sites (inactive repressor) • trp bound (2) recognition helices 34Å apart for proper binding of DNA (active repressor) TA: Christine Feng Zinc Finger Motif • 1 α helix & 2 β strands coordinated by a Zn metal (stabilized by 2 Cys, 2 His – midterm 6a) • Approximately 30 amino acids • Highly conserved coordination sites (recall: midterm question 6b) • Proteins contain anywhere from 1 ­60 zinc finger motifs within sequence • α helix side chains H ­bond with base pairs of DNA (midterm 6c) • Fig 10.3 – schematic diagram of 3 Zn fingers binding in tandem to major groove Leucine Zipper Motif – midterm question 9 • 2 amphipathic α helices that interact to form a coiled ­coil (recall: Ch 3) • Heptad repeat: almost all 4th residue is Leucine (fig 10.17) • Hydrophobic core is major contributing factor to stability • Distal (basic) region on each helix interacts with major groove of DNA [email protected] Section: Mon 4-5 Center 205 OH: Wed 11-12 Geisel S&E CAP – catabolite gene activating protein • DNA binding protein that assists RNA polymerase in effective binding o Promotes initiation of RNA synthesis • Functions as dimer • Activated by cAMP (allosteric effector) • Interacts directly with base pairs & phosphate groups • Bending of DNA contributes to activation of transcription ...
View Full Document

{[ snackBarMessage ]}

Ask a homework question - tutors are online