Deck 22: Homologous Recombination

Question 1

During mating between two strains of Neurospora crassa containing different alleles of the same gene one would expect a 1:1 genotypic ratio in progeny spores,however,approximately 0.1% of the time this ratio strays from the predicted.This phenomenon is called_____________ ___________________.

Answer 1

gene conversion

Question 2

RecBCD protein has ______________ activity that can nick dsDNA.

Answer 2

endonuclease

Question 3

During postsynapsis strand exchange in homologous recombination of E.coli,ATP is necessary for _______ clearance from the synapsing DNA.

Answer 3

RecA

Question 4

A ________ double helix is different than a Watson-Crick double helix in that the two strands are aligned side by side instead of intertwined.

Question 5

West and colleagues used gel mobility shift assays to demonstrate that __________ could bind to and resolve Holliday junctions.

A)RecA
B)RuvA
C)RuvB
D)RuvC
E)RecB

Question 6

Spo11 creates __________ in DNA during homologous recombination in Saccharomyces cerevisiae.

Question 7

David Gonda and Charles Radding have provided experimental evidence that the minimum degree of homology necessary for efficient synapsis to occur during homologous recombination is between 30 and 151 bp.

Question 8

Which of the following statements is not true concerning homologous recombination?

A)It can be intramolecular.
B)It can be bimolecular.
C)Only one cross-over event can occur.
D)It results in genetic variation.
E)It is a reciprocal event.

Question 9

In eukaryotes,_______ often includes homologous recombination as a way to increase genetic variation.

Question 10

________________ recombination is a cross-over event that joins previously separated DNA segments.

Question 11

Molecular modeling of RuvA and a Holliday junction showed that they form a _________ that favors rapid branch migration.

A)square planar conformation
B)L-shape conformation
C)clover leaf conformation
D)D loop conformation
E)Y-shape conformation

Question 12

Branch migration is a spontaneous process that takes place after a Holliday junction is formed.

Question 13

The role of SSB in RecBCD homologous recombination appears to be to unwind the secondary structures found in dsDNA.

Question 14

RuvA and RuvB are involved in ________ of a Holliday junction during homologous recombination.

Question 15

________resolvase clips DNA at the consensus sequence,5'-(A/T) $\downarrow$ (G/C)-3'during RecBCD recombination repair.

Question 16

Which of the following techniques was key in demonstrating the presynapsis and synapsis steps of homologous recombination?

A)S1 nuclease mapping
B)exonuclease digestion
C)DNA footprinting
D)Southern Blot
E)electron microscopy

Question 17

Holliday junctions are intermediates in RecBCD recombination in E.coli.

Question 18

The E.coli genome,on average,contains approximately __________chi sites that can be involved in homologous recombination.

Question 19

One mechanism by which gene conversion can occur in N.crassa during meiosis is _______.

A)RecBCD
B)mismatch repair
C)double stranded break synthesis
D)SOS repair
E)excision repair

Question 20

___________ protein greatly enhances the binding of RecA to single stranded DNA.

Question 21

Double stranded break formation in mitotic recombination is followed by 3' $\rightarrow$ 5' exonuclease digestion of 3' ends at the break to yield 5' overhangs.

Question 22

All organisms undergo homologous recombination as a way to increase genetic variation and help cope with DNA damage.

Question 23

A conserved tyrosine residue is likely to be the catalytic amino acid in Spo11 and homologous proteins.

Question 24

ATP $\gamma$ S is an unhydrolyzable ATP analog that was used along with glutaraldehyde by Parsons and West to trap Holliday junctions for gel mobility shift assays.

Question 25

Gene conversion usually only occurs between nonallelic genes such as the MAT genes used to determine mating type in yeasts.

Question 26

Branch migration is not necessary for efficient resolution of Holliday junctions.

Question 27

Since RecA is such a versatile protein,RecBCD is not really necessary for homologous recombination to occur.

Question 28

Both RuvA and RuvB have ATPase activity that drives the unwinding and rewinding of DNA during branch migration.

Question 29

E.coli RecA protein is only necessary for the presynapsis step of homologous recombination.

Question 30

Mutations in ruvC increase sensitivity to UV light due to defective recombination repair.