Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57a bStructure and binding of tetrameric lac repressor proteinhinge + helix-turn-helixIPTG (isopropylthioglucose)CH2SOHHOHOOHOtruncation at hingetruncation at hingetruncation at point of hinge attachmentTetramer, with two of the tetrameric units selectedB. Rotated 90o around core axisHeadpiece (hinge + HTH motif)A. Looking down DNA helixLac repressor dimer bound to operatoranti-inducero-nitrophenylfructose (ONPF)hingeLac repressor + IPTG truncated at hinge.Lac repressor + ONPF truncated at oligomerization domainContrast inducer-bound and active lac repressorOOOOHPONNNH2NNOcyclic AMP (cAMP)E. coli CAP +cAMP + DNA HTH motifcAMPATATAA = consensus sequence of TATA boxstart point at: Py2CA Py5TFIIDHuman TBP complexed at TATA box of DNAGGCATATATATC5'3'octamerCAATGCTATAstart pointDNA binding motif of steroid receptorsZn fingersOther DNA binding motifsHelix-turn-helixHelix-loop-helixAdditional motif often present in transcription factorsLeucine zippers -Cys-X2-4-Cys-X3-Phe-X5-Leu-X2-His-X3-His-The zinc finger motif is:C-terminalN-terminalZn finger fragment bound to DNAHormone binding and dimerization regions vary from 5-15%C-terminalN-terminalfingerDNA bindingdimerizationGLUCOCORTICOID RECEPTOR FRAGMENT BOUND TO DNAhomeodomainHelix-turn-helix binding motif#3, C-terminal#1, N-terminal#3#2#1bHLH DNA binding motif of transcription factor MyoDbasic region binding DNAhelix 1helix 2CREB-DNA complexLeu selected in zipper domainArg selected in DNA-binding domainChains: blue = c-Fos, green = c-JunResidues: red = Leu, purple = ArgHuman protooncogenes c-Jun:c-Fos heterodimerHNNNNOH2NNNNNOH2NHNNNNOHH2NNNNNOHNHHN NOOHHNNNNOH2NNNNNOH2NHNNNNOHH2NNNNNOHNHHN NOOHHNNNNOH2NNNNNOH2NHNNNNOHH2NNNNNOHNHHN NOOHH3CKeto-enol tautomerization of Guaketo form (normal)enol formpairing properties of enolPoint mutation, transitionpyrimidinepyrimidinepurinepurinePoint mutation, transversionpyrimidinepurinepurinepyrimidineG-T  G-C + A-TG-C  C-G, T-A  A-T, G-C  T-Anonsense mutation occurs when a termination codon is generatedmissense mutation occurs when a different amino acid is codedG-T  G-C + A-TOne round of replication on mismatched strands “fixes” the mutation.3'-G-p-G-p-G-p-G-p-G-p-G-5' 3'-G-p-G-p G-p-G-p-G-p-G-5'5'-C-p-C p-C-OH 5'-C-p-C-p-C-OHp-CG-pMechanism for frameshift mutationsATA GCA ACC GGC CTT ACA AAT TCATA GCA ACC GCC TTA CAA ATT CChange of reading frame following the location of a deletioninsertion deletion[2] Note that this suppressor tRNA can still recognize the wild-type Trp codon as well as the UGA codon.[1] The suppression efficiency varies for different sites because the mRNA sequence following the nonsense codon influences how well the suppressor tRNA works. Modified from Miller (1992).0.1-30%[2]trpTtRNATrpCCA --> UCAOpaltrpTglyTtRNAGlyUCC --> UCAOpalglyTtyrUtRNATyrGUA --> UUAOchresupMtyrTtRNATyrGUA --> UUAOchresupClysVtRNALysUUU --> UUAOchresupNlysTtRNALysUUU --> UUAOchresupLglnUtRNAGlnUUG --> UUAOchresupBtyrUtRNATyrGUA --> CUAAmbersupZ11-100%tyrTtRNATyrGUA --> CUAAmbersupFtrpTtRNATrpCCA --> CUAAmbersupU6-54%serUtRNASerCGA --> CUAAmbersupD30-100%leuXtRNALeuCAA --> CUAAmbersupP0.8-20%glnVtRNAGlnCUG --> CUAAmbersupEEfficiency[1]GenetRNAAnticodon changeTypeSuppressorSuppressor tRNAs from E. coliOOOOPOOOHNOOOOCH3CH3HNOthymine-thymine dimerT THHHHHOOHHHHOPOOOOOOPOOBBase-Eliminationabasic siteFp tehuman 8-oxoguanine glycosylase (hOGG1)Complex with DNA containing 8-oxoGua8-oxoGuaHNNNHNOH2NO8-oxoguanineLysine at 249 displaces 8-oxoGua from C1’ (arrow)H2NOglutamineH2NlysineC1'HUMAN MITOCHONDRDIAL URACIL GLYCOSYLASE (UDG), WITH GLYCOSIDIC LINKAGE HYDROLYZEDhuman alkyladenine glycosylase (AAG)complex with DNA modified by tricyclic base 1,N6-AdeNNNNNdR1,N6-dAdoAAG catalyses deglycosylation by a water bridge to GluHolliday junctionEukaryotic homologues to RecA are characterized in yeast: DMC1 and RAD51BACTERIAL REPAIR BY