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A pair of ZFNs, each with three zinc fingers binding to target DNA, are shown introducing a double-strand break, at the FokI domain, depicted in yellow. Subsequently, the double strand break is shown as being repaired through either homology-directed repair or non-homologous end joining. [3]
In addition to histidine, a conserved arginine on the second beta strand of the zinc fingers makes contact with the phosphodiester oxygen on the DNA strand. [25] [26] [29] Also serine 75 on the third finger hydrogen bonds to the phosphate between base pairs 7 and 8, as the only backbone contact with the secondary strand of DNA. [25] [26] [29]
Zinc fingers were first identified in a study of transcription in the African clawed frog, Xenopus laevis in the laboratory of Aaron Klug.A study of the transcription of a particular RNA sequence revealed that the binding strength of a small transcription factor (transcription factor IIIA; TFIIIA) was due to the presence of zinc-coordinating finger-like structures. [6]
A double-strand break repair model refers to the various models of pathways that cells undertake to repair double strand-breaks (DSB). DSB repair is an important cellular process, as the accumulation of unrepaired DSB could lead to chromosomal rearrangements, tumorigenesis or even cell death. [ 1 ]
After strand invasion, the further sequence of events may follow either of two main pathways discussed below (see Models); the DSBR (double-strand break repair) pathway or the SDSA (synthesis-dependent strand annealing) pathway. Homologous recombination that occurs during DNA repair tends to result in non-crossover products, in effect restoring ...
In addition, it has been used to engineer stably modified human embryonic stem cell and induced pluripotent stem cell (IPSCs) clones and human erythroid cell lines, [11] [28] to generate knockout C. elegans, [12] knockout rats, [13] knockout mice, [29] and knockout zebrafish. [14] [30] Moreover, the method can be used to generate knockin organisms.
The DNA is cut 9 nucleotides downstream of the motif on the forward strand, and 13 nucleotides downstream of the motif on the reverse strand, [3] producing two sticky ends with 4-bp overhangs. Its molecular mass is 65.4 kDa, being composed of 587 amino acids.
Rad51 protein is recruited and binds in a protein complex to search for a complementary sequence analogous to double-strand-break repair. The filament searches for the homologous chromosome, strand invasion occurs where the new chromosome forms a D-loop over the bottom sister chromatid, then the ends are annealed.