What is the purpose of NHEJ?

Key Points Mammalian non-homologous DNA end joining (NHEJ) is the primary pathway for the repair of DNA double-strand breaks (DSBs) throughout the cell cycle, including during S and G2 phases. NHEJ relies on the Ku protein to thread onto each broken DNA end.

What phase is NHEJ?

G1 phase
Most of the NHEJ-deficient cell lines are hypersensitive in G1 phase, leading to conclusion that NHEJ acts primarily in G1. NHEJ has been proposed to act also in S-phase 24, 25, or in all cell cycle stages 10, 11.

What is HDR and NHEJ?

HDR is a precise repair mechanism that uses homologous donor DNA to repair DNA damage, whereas NHEJ is an error-prone mechanism in which broken ends of DNA are joined together, often resulting in a heterogeneous pool of insertions and deletions.

How does NHEJ repair DNA?

NHEJ mediates the direct religation of the broken DNA molecule (5). It has the potential to religate any type of DNA ends and unlike the other classically studied DSB repair mechanism, homologous recombination (HR), NHEJ does not require a homologous template for repair of the DNA lesion.

What are the two fundamental components of NHEJ?

The core components of NHEJ [Ku (Yku), XLF (Nej11), XRCC4 (Lif1), and ligase 4 (Dnl4) (Table 1)] are conserved in the eukaryote S. cerevisiae (hereafter referred to generally as ‘yeast’).

What is Alt NHEJ?

Alternative NHEJ (alt-NHEJ) refers to more recently described mechanism(s) that repair DSBs in less-efficient backup reactions. There is great interest in defining alt-NHEJ more precisely, including its regulation relative to c-NHEJ, in light of evidence that alt-NHEJ can execute chromosome rearrangements.

What is NHEJ Crispr?

Clustered regularly interspaced short palindromic repeat (CRISPR)–CRISPR-associated protein (Cas) systems generate a highly specific double-strand break at the target site that can be repaired via nonhomologous end joining (NHEJ), resulting in the desired genome alteration.

Is NHEJ or HDR better?

At its core, NHEJ-break ends can be ligated without a homologous template, whereas HDR-breaks requires a template to guide repair. NHEJ is a very efficient repair mechanism that is most active in the cell. It is also susceptible to frequent mutation errors due to nucleotide insertions and deletions (indels).

What is the difference between NHEJ and HR?

NHEJ modifies the broken DNA ends, and ligates them together with no regard for homology, generating deletions or insertions [2]. In contrast, HR uses an undamaged DNA template to repair the break, leading to the reconstitution of the original sequence [3].

What is NHEJ repair?

Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as “non-homologous” because the break ends are directly ligated without the need for a homologous template, in contrast to homology directed repair, which requires a homologous sequence to guide repair.

What is NHEJ CRISPR?

What is C NHEJ?

Abstract. To investigate the fidelity of canonical non-homologous end joining (C-NHEJ), we developed an assay to detect EJ between distal ends of two Cas9-induced chromosomal breaks that are joined without causing insertion/deletion mutations (indels).

Is HDR or NHEJ better?

What happens after NHEJ?

During NHEJ, KU protein heterodimer is recruited to DNA ends followed by DNA-PKcs in association with ARTEMIS, which processes DSBs. Pol μ and/or λ fills these ends, when required, followed by ligation using XLF–XRCC4–DNA Ligase IV complex.

How does NHEJ work in CRISPR?

CRISPR Induces DNA Repair Pathways: NHEJ, HDR, and Beyond. CRISPR works by targeting a precise location in the genome and then cutting both strands of DNA, generating a double-strand break (DSB) at that particular spot. As cells cannot survive for long with cut DNA, their alarm bells go off whenever a break occurs.

Can NHEJ cause insertion?

While classical NHEJ (C-NHEJ) can result in perfect repair, small insertions/deletions are also possible.

What is the danger of NHEJ?

NHEJ can be error prone when re-ligating the free ends, so small insertions or deletions (indels) are often made at the lesion site. Imprecise repair of the DSB via NHEJ is very efficient in zebrafish and other model systems, and this pathway is commonly used to create targeted mutations.

Is NHEJ found in all bacteria?

In bacteria. Many species of bacteria, including Escherichia coli, lack an end joining pathway and thus rely completely on homologous recombination to repair double-strand breaks. NHEJ proteins have been identified in a number of bacteria, however, including Bacillus subtilis, Mycobacterium tuberculosis, and Mycobacterium smegmatis.

What is the difference between yeast and mycobacteria with NHEJ?

In mycobacteria, NHEJ is much more error prone than in yeast, with bases often added to and deleted from the ends of double-strand breaks during repair. Many of the bacteria that possess NHEJ proteins spend a significant portion of their life cycle in a stationary haploid phase, in which a template for recombination is not available.

What is NHEJ and how does it work?

NHEJ is typically guided by short homologous DNA sequences called microhomologies. These microhomologies are often present in single-stranded overhangs on the ends of double-strand breaks. When the overhangs are perfectly compatible, NHEJ usually repairs the break accurately.

Is NHEJ in vertebrates similar to that in invertebrates?

NHEJ in yeast, which appears to be similar for plants and invertebrates, has been thoroughly reviewed as well (24, 25). Hence, the discussion here will focus on NHEJ in vertebrates, with appropriate comparisons to prokaryotic and yeast NHEJ.