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that triggers a major change in the activities of this enzyme. Upon encountering the Chi sequence as it unwinds DNA, RecBCD cuts the DNA a few nucleotides to the 3’ side of Chi, within the important sequences noted above; depending on the reaction conditions, this cut is either a simple nick on the
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by cutting of the D-loop and a second exchange of DNA strands; the
Holliday junction can be converted into linear duplex DNA by cutting of the Holliday junction and ligation of the resultant nicks. Either type of resolution can generate recombinant DNA molecules if the two interacting DNAs are
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3'-ended strand or the change of nuclease activity from cutting the 3’-ended strand to cutting the 5’-ended strand. In either case the resulting 3’ single-stranded DNA (ssDNA) is bound by multiple molecules of
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protein that facilitate "strand invasion," in which one strand of a homologous double-stranded DNA is displaced by the RecA-associated ssDNA. Strand invasion forms a joint DNA molecule called a
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Taylor AF, Amundsen SK, Smith GR (2016) Unexpected DNA context-dependence identifies a new determinant of Chi recombination hotspots. Nucleic Acids Res. 44(17):8216-28.
121:. Resolution of the D-loop is thought to occur by replication primed by the 3’ end generated at Chi (in the D-loop). Alternatively, the D-loop may be converted into a
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Amundsen SK, Sharp JW, Smith GR (2016) RecBCD Enzyme "Chi
Recognition" Mutants Recognize Chi Recombination Hotspots in the Right DNA Context. Genetics 204(1):139-52.
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plus important nucleotides about 4 to 7 nucleotides to the 3' side of the core sequence. The existence of Chi sites was originally discovered in the genome of
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Amundsen SK, Taylor AF, Reddy M, Smith GR. (2007). Intersubunit signaling in RecBCD enzyme, a complex protein machine regulated by Chi hot spots.
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Smith GR. (2012). How RecBCD Enzyme and Chi
Promote DNA Break Repair and Recombination: a Molecular Biologist's View.
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Chi sites are sometimes referred to as "recombination hot spots". The name "Chi" is an abbreviation of
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Dillingham MS, Kowalczykowski SC. (2008). RecBCD enzyme and the repair of double-stranded DNA breaks.
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is more likely to occur than on average across the genome. Chi sites serve as stimulators of DNA
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phage lambda, the term is sometimes written as "χ site", using the Greek letter
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of the Chi site is unique to each group of closely related organisms; in
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and other enteric bacteria, such as
Salmonella, the core sequence is
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genetically different, as well as repair the initially broken DNA.
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Stahl FW. (2005). Chi: A little sequence controls a big enzyme.
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246:Homologous Recombination Interactive Animation
153:and other bacteria the term "Chi" is proper.
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248:, online artwork from Trun N and Trempy J,
104:The Chi sequence serves as a signal to the
59:or chemical treatments, or result from
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55:in bacteria, which can arise from
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250:Fundamental Bacterial Genetics
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141:nstigator. In reference to
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53:double-strand break repair
49:homologous recombination
198:Microbiol Mol Biol Rev.
184:Microbiol Mol Biol Rev.
35:is a short stretch of
87:bacteriophage lambda
214:21(24): 3296-3307.
228:170(2): 487–493.
123:Holliday junction
16:(Redirected from
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200:72(4): 642-671.
63:breakage during
61:replication fork
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33:Chi sequence
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18:Chi sequence
47:near which
260:Categories
157:References
81:-GCTGGTGG-
212:Genes Dev
133:rossover
108:helicase-
57:radiation
45:bacterium
271:Genetics
234:15980270
226:Genetics
220:18079176
206:19052323
192:22688812
178:27330137
168:27401752
110:nuclease
101:genome.
69:sequence
29:Chi site
151:E. coli
143:E. coli
137:otspot
99:E. coli
95:E. coli
74:E. coli
39:in the
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106:RecBCD
67:. The
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91:virus
43:of a
230:PMID
216:PMID
202:PMID
188:PMID
174:PMID
164:PMID
115:RecA
89:, a
147:chi
37:DNA
31:or
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83:3'
79:5'
27:A
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139:i
135:h
131:c
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