telomeric D-loop disassembly

Definition

Target type: biologicalprocess

A telomere loop disassembly process that results in the disassembly of telomeric D-loops. A telomeric D-loop is a three-stranded DNA displacement loop that forms at the site where the telomeric 3' single-stranded DNA overhang (formed of the repeat sequence TTAGGG in mammals) is tucked back inside the double-stranded component of telomeric DNA molecule, thus forming a t-loop or telomeric-loop and protecting the chromosome terminus. [GOC:BHF, GOC:BHF_telomere, GOC:nc, PMID:10338204, PMID:24012755]

Telomeric D-loop disassembly is a crucial step in the replication and maintenance of telomeres, the protective caps at the ends of eukaryotic chromosomes. This process involves the resolution of a complex structure called the D-loop, which is formed during telomere replication.

The D-loop arises when the leading strand of the lagging strand template invades the duplex telomere, displacing one of the strands and forming a three-stranded structure. This invasion is facilitated by the telomere-specific proteins, including the shelterin complex, which binds to the telomeric DNA and promotes its unwinding and invasion.

The D-loop disassembly process involves several key steps:

1. **Unwinding of the D-loop:** The D-loop is unwound by the helicase activity of the telomere-specific protein, **RTEL1**. RTEL1 is a 3'-5' helicase that can unwind both DNA and RNA:DNA hybrids, making it ideal for resolving the complex D-loop structure.

2. **Resolution of the D-loop:** The displaced strand is then processed by the **exonuclease activity** of the telomere-specific protein **EXO1**. EXO1 degrades the 5' flap of the D-loop, removing the invading strand and restoring the original duplex telomere.

3. **Re-ligation of the telomere:** The 3' overhang generated by EXO1 is then re-ligated to the complementary strand by the telomere-specific DNA ligase **LIG4**. This step ensures that the telomere is fully restored and protected from degradation.

The telomeric D-loop disassembly process is tightly regulated, and its disruption can lead to telomere shortening, chromosome instability, and cellular senescence. This process is essential for maintaining telomere integrity and ensuring proper chromosome replication and segregation during cell division.'
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Proteins (3)

Compounds (3)