Double-strand break made in recipient 14 Double-strand breaks initiate Break is enlarged to gap with 3'ends recombination 3'end migrates to other duplex 量HHH Figure 14.5 Synthesis from 3 end disp la ces one strand in gap Recombination is HHHHHHI initiated by a double Displaced strand migrates to other duplex trand break, followed HHHHHHHHHHHHHHHHHHHH by formation of single DNA synthesis occurs from other 3'end tranded3￠ends,One THHHHHHHHTHHA of which migrates to a H homologous duplex Gap replaced by donor seq Reciprocal migration generates double crossov 消当 HHHHHHHE
Figure 14.5 Recombination is initiated by a doublestrand break, followed by formation of singlestranded 3￠ ends, one of which migrates to a homologous duplex. 14.3 Double-strand breaks initiate recombination
14.4 Double-strand breaks initiate synapsis Chrom atin I Lateral elem er Central elem ent Heinel I Chrom atin Figure 14.6 The synaptonemal complex brings chromosomes into juxtaposition. This example of Neotellia was kindly 请莘大 provided by m. Westergaard and D. Von Wettstein
Figure 14.6 The synaptonemal complex brings chromosomes into juxtaposition. This example of Neotellia was kindly provided by M. Westergaard and D. Von Wettstein. 14.4 Double-strand breaks initiate synapsis
14.4 Double-strand breaks initiate synapsis Site-specific double-strand breaks Joint Recom binant molecules molecules Molecular events Appear Disappear ersist Time (m inutes)匚20406080100120140160180200220 Cytological events DNA Axial Synaptonemal Synapt onem al replication elem ents complexes complexes ends form dissociate Stage of meiosis Lept otene Zygotene Pachytene> Diploter Figure 14.7 Double-strand breaks appear when axial elements form, and disappear during the extension of synaptonemal complexes. Joint molecules appear and persist until DNA recombinants are detected at the end of pachytene 请莘大
Figure 14.7 Double-strand breaks appear when axial elements form, and disappear during the extension of synaptonemal complexes. Joint molecules appear and persist until DNA recombinants are detected at the end of pachytene. 14.4 Double-strand breaks initiate synapsis
14 4 Double-strand 人AA breaks initiate Reversible clava nt↓ synapsis sp011 sp011 Figure 14.8 Spoll is Dissociation of complex covalently joined to / the5￠ ends of Removal of spo11 double-strand breaks followed by nuclease attack 消当 5NNe33④5
Figure 14.8 Spo11 is covalently joined to the 5￠ ends of double-strand breaks. 14.4 Double-strand breaks initiate synapsis
RecBcd binds a double-strand break 14 5 The bacterial RecBCD systemis RecBCD unwinds degrades DNA as exonuclease stimulated by chi sequences RecBcD endonuclease cleaves sin gle str and at chi Figure 14.9 RecBCD nuclease approaches a chi RecD dissociates at chi sequence sequence from one side, degrading DNa as it proceeds; at the chi site, it makes an endonucleolytic cut. loses recd. and retains RecBc continues as helicase only the helicase activity 消当
Figure 14.9 RecBCD nuclease approaches a chi sequence from one side, degrading DNA as it proceeds; at the chi site, it makes an endonucleolytic cut, loses RecD, and retains only the helicase activity. 14.5 The bacterial RecBCD system is stimulated by chi sequences