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mes R

esearch Center

Homing Endonucleases

Sequence nearly identical to the carrot vma1 gene – except for central region of about 1200 nucleotides.

Homing

Ribonucleotide Reductase

InteinGroup I IntronsGroup II Introns

Inteins

Group I Introns

Group II Introns

Homing cycle of a parasitic genetic element (modified from [3, 13]). Recent findings suggest that due to complex population structure the cycle might not operate in synchrony in different subpopulations. The red arrows indicate the trajectory of the functioning HE and the black arrows the fate of the host gene. The precise loss can occur through recombination with an intein or intron free allele, or, in case of introns, through recombination with a reverse transcript of the spliced mRNA [39, 40].

From: Gogarten et al., Annu. Rev. Microbiol. 2002. 56:263–87

XXAlleles with empty

Target Site

ZZAlleles invaded by a functional Homing

Endonuclease

YYAlleles harboring a

dysfunctional Homing

Endonuclease

(I) X-alleles are converted to Z-

alleles through the function of

the homing endonuclease,

leading to super Mendelian

inheritance of Z

X < Z

Y > Z(II) Carriers of the Y-allele are more fit than carriers of the Z

allele. The presence of a dysfunctional homing endonuclease provides

immunity to invasion by Z

(III)

Carri

ers o

f the

Y-all

ele ar

e

less fi

t tha

n ca

rrier

s of t

he X

allele

. Y <

X

Long term persistence of the HE containing allele is possible within a single well mixed population. Different trajectories result depending on the size of the selective disadvantage caused by the functioning HE and the frequency of efficient homing.

Collaboration with Adi Barzel, Uri Obolski, Martin Kupiec, Lilach Hadany from Tel Aviv University