What is Holliday model of recombination?
In 1964, Robin Holliday proposed a model that accounted for heteroduplex formation and gene conversion during recombination. It illustrates the critical steps of pairing of homologous duplexes, formation of a heteroduplex, formation of the recombination joint, branch migration and resolution.
What is a Holliday junction in DNA?
Holliday junction, cross-shaped structure that forms during the process of genetic recombination, when two double-stranded DNA molecules become separated into four strands in order to exchange segments of genetic information.
What are the steps of Holliday junction formation?
The key features of this model are diagrammed in the steps in Figure 19-14: (1) a double-strand break, followed by digestion of the 5′ end of both cut sites; (2) the invasion by a remaining 3′ tail of the uncut other duplex; (3) the repair synthesis of one strand; (4) the repair synthesis of the other strand, and …
How is Holliday junction resolved?
(1996) Resolution of Holliday junctions in genetic recombination: RuvC protein nicks DNA at the point of strand exchange. Proc Natl Acad Sci USA 93(22):12217–12222. (1997) The RuvC protein dimer resolves Holliday junctions by a dual incision mechanism that involves base-specific contacts.
What is Holliday junction resolving enzyme?
Holliday junction-resolving enzymes are nucleases that are highly specific for the structure of the junction, to which they bind in dimeric form. Two symmetrically disposed cleavages are made.
What does the resolution of Holliday junctions mean?
Holliday junction (HJ) resolution is essential for chromosome segregation at meiosis and the repair of stalled/collapsed replication forks in mitotic cells. All organisms possess nucleases that promote HJ resolution by the introduction of symmetrically related nicks in two strands at, or close to, the junction point.
Why is Holliday junction important?
Holliday junctions provide a covalent link between recombining DNA molecules and need to be removed prior to chromosome segregation at mitosis. Defects in their resolution lead to mitotic catastrophe, characterized by the formation of DNA breaks and chromosome aberrations.
Which type of DNA is connected by Holliday junction Mcq?
Which type of DNA is connected by a holiday junction? Explanation: Finishing of recombination usually requires resolution of the holiday junction by cutting the DNA strand. Two homologous DNA duplex is connected by a single holiday junction.
Which proteins function in the resolution of Holliday junctions?
RuvC is a dimeric protein that promotes HJ resolution by introducing a pair of symmetrically related nicks in two strands that lie diametrically opposed across the junction point.
Which enzyme cuts DNA at Holliday junction?
Holliday junction cleavage, which generates two unconnected DNA duplexes, is catalyzed by a group of structure-selective endonucleases called HJ resolvases. These nucleases have been isolated from bacteria, bacteriophages, archaea, viruses, yeasts, plants, and mammals (Table 1) and share a number of common properties.
Why does Holliday junction occur?
Cleavage, or resolution, of the Holliday junction can occur in two ways. Cleavage of the original set of strands leads to two molecules that may show gene conversion but not chromosomal crossover, while cleavage of the other set of two strands causes the resulting recombinant molecules to show crossover.
How is the Holliday model used in homologous recombination?
The Holliday model for homologous recombination Single-strand nicks are introduced at the same position on both parental molecules. The nicked strands then exchange by complementary base pairing, and ligation produces a crossed-strand intermediate called a Holliday junction. 15.
What are the steps in the recombination of DNA?
Key steps of HR 1. Alignment of two homologous DNA molecules 2. Introduction of breaks in the DNA 3. Formation of initial short regions of base pairing between the two recombining DNA molecules. 4. Strand invasion. 5. Formation of Holliday junction & Cleavage of the Holliday junction 15.
How does ligation complete the formation of a Holliday junction?
(e) Ligation completes the formation of a Holliday junction, which is genetically asymmetric in that only one of the two duplexes has a region of potentially heteroduplex DNA. If the junction migrates, heteroduplex DNA can arise on both duplexes. (f) Resolution of the junction occurs as in the Holliday model.
How is isomerization and resolution of Holliday junctions resolved?
Isomerization and resolution of Holliday junctions Holliday junctions are resolved by cutting and rejoining of the crossed strands. If theHolliday junction formed by the initial strand exchange is resolved, the resulting progeny are heteroduplexes but are not recombinant for genetic markers outside of the heteroduplex region.