Double-strand break made in recipient 14.3 Double-strand HHHHHHHHHHHHHHHHHHHHHHHHH HHHHHHHHHHHHHHHH breaks initiate Break is enlarged to gap with 3'ends HHHHHHHHHHHHHHHHHHHHHHHH recombination HH四 小田 3'end migrates to other duplex 出 HHHHHHH HH Figure 14.5 Synthesis from 3'end displaces one strand in gap Recombination is HHHHHHHHHHHHHHHHHHHH h HHHHHHHH ,出 initiated by a double- Displaced strand migrates to other duplex strand break,followed WH中 HHHHH H网 by formation of single- DNA synthesis occurs from other 3'end stranded3￠ends,one HHHHHHHHHHHHHHHHHHHHHHH of which migrates to a HHHHH 出 homologous duplex. Gap replaced by donor sequence Reciprocal migration generates double crossove 清苇大当 HHHH+HHHHHIn nH
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 Lateral elem ent Central elem en ateral elem Chrom atin Figure 14.6 The synaptonemal complex brings chromosomes into juxtaposition.This example of Neotellia was kindly 情華大当 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 Persist Time (minutes) 204060 80100120140160180200220 Cytological events DNA Axial Synaptonemal Synaptonem al replication elem ents complexes complexes ends form form dissocate Stage of meiosis Leptotene Zygotene Pachytene Diplotene 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. 清菜大当
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 八入八入入 breaks initiate Reversible cleavage synapsis Sp011 5入八八 八NN5 Sp011 Figure 14.8 Spol1 is Dissociation of complex covalently joined to 5N八八o the5Φends of Removal of Spo11 double-strand breaks. followed by nuclease attack 情華大当
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 3 RecBCD system is RecBCD unwinds degrades DNA as exonuclease stimulated by chi HHHHHHHHHHHHHm sequences RecBCD endonuclease cleaves single strand at ch Figure 14.9 RecBCD HHHHHHHHhmmmomom 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 ttttttthawwwnw cut,loses RecD,and retains RecBC continues as helicase only the helicase activity 清苇大当
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