Baker lecture Notes - Bisc 320, Molecular Biology lecture...

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Bisc 320, Molecular Biology lecture notes, Fall, 2007.Week 8:Molecular GeneticsSome notes on:Conservative site-specific recombination and transposonsSee also, Watson, et al., chapter 11.> 40% of severe hemophilia A is caused by an inversion in exon #22 in the 26 exonfactor VIII gene.Leukemias: reciprocal exchange of exons between chromosomes.Transposon terminal d.s. DNA sequences:IR:Inverted repeats (palindromes) allow inversions to occur via: IR--------IRDR:Direct repeats: deletions (excisions) and insertions occur via DR---------DRFigs 11-1, 11-11-2, 11-3DNA-protein synaptic complexes form at pairs of recombinant recognition sequences.Conservative site-specific recombinases:Table 11-1, Fig 11-51.Serine type:cause d.s. breaks; intermediate is anon-Holliday, non-heteroduplex,structure having a free 3’OH on each d.s. DNA piece, with a monomeric serine proteinhooked to the 5’ end of the two DNA strands.No ATP needed.Staggered breaks(nicks)in each of the d.s. DNAs.Four recombinase monomers are used inrecombination between two DNA duplexes.Recombination is via swapping of left andright s.s. overhangs of the four ends.Fig 11-6a.Salmonella Hin invertase can invert a segment of bacterial genomic DNA.Beforeflip, in parenthesis:(hixL hin P hixR)flijB flijA, is in the “on” rightward-xcriptionconfiguration, that allows flijA expression.If there is a flip to the “off” configeration,transcription from P is then to the left.hixL and hixR are 60 BP each and palindromic toeach other.Fis (factor for inversion stimulation) bends DNA.4 Hin/2 Fis complex withHU protein forms at hix sites.(HU, unlike IHF is sequence independent.)flijB encodesH2 flagellin; flijA encodes repressor of distant flagellin gene.“On” allows only H2-typeof flagella; “off” causes H1 flagella to appear on bacterial surfaces.This switch mayelude the mammalian immune system by changing the type of flagella exposed onbacterial surfaces.Food poisoning.Fig 11-11, 11-12, 11-132.Tyrosine type:cause s.s breaks; intermediate is aHollidaystructure with a proteinmonomer hooked via tyrosine to the 3’ ends of nicks.Rotation of structure producesrecombinant.Four monomers are used in recombination between two DNA duplexes.An acidic DDE (aspartate, aspartate, glutamate) motif is often found in tyrosinerecombinase proteins, such as MuA, TN5, and RSV integrase:NH2---DNA binding site---DDE---protein-protein binding site—COOHFig 11-7a.P1 bacteriophage Cre protein acts at pairs of loxsites, creating a deletion of the loxsequences and the intervening DNA:Four subunits of Cre create a Holliday structure,prior to the deletion event.Fig 11-8b.Lambda bacteriophage:lysogenic state vs lytic growth after viral infection.Afterinfection, linear d.s. lambda DNA circularizes via 12/12 s.s. DNA overlap. Integration ofthe new lambda DNA circle is via a Holliday structure, with crossing over at:PP’ X BB’
There is sequence homology between 7 out of the 15 base pairs at this crossover site.

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Term
Summer
Professor
Baker,Aparicio
Tags
molecular biology, Genetics, Molecular Genetics, DNA, Biology Lecture Notes, Molecular Biology lecture

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