5 - TA: Christine Feng hufeng@ucsd.edu Section: Mon 4-5...

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Unformatted text preview: TA: Christine Feng hufeng@ucsd.edu 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 hufeng@ucsd.edu 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 ...
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This note was uploaded on 02/17/2010 for the course BIBC BIBC 100 taught by Professor Buehler during the Spring '09 term at UCSD.

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