Insertiedeletielussen

Insertiedeletielussen are unpaired DNA loops that form on one strand of a double helix when the two strands misalign during DNA replication or repair. The term describes insertion–deletion loops (IDLs), often occurring in regions rich in short tandem repeats. An IDL arises when extra nucleotides on one strand fail to pair with the opposite strand, creating a small loop in the duplex that can persist through replication if not promptly repaired.

Formation typically involves polymerase slippage in repetitive sequences, which can cause the nascent strand to misalign with the template. Depending on whether the loop is on the template or the newly synthesized strand, the cellular outcome is a small insertion or a deletion in subsequent copies of the DNA. IDLs are a normal byproduct of replication in repetitive DNA, but their persistence can lead to genetic variation or functional consequences.

Biologically, IDLs contribute to mutations in microsatellite regions and can drive frameshifts if they occur within coding sequences. They are especially relevant in cancer, where instability at microsatellites (microsatellite instability) reflects defects in the DNA mismatch repair system. In healthy cells, IDLs are largely corrected by repair pathways; in repair-deficient cells, they accumulate and can affect gene regulation and genome stability.

Repair and detection methods focus on the mismatch repair system, notably the MutSα and MutSβ complexes, which recognize IDLs and coordinate excision and resynthesis. Detection of IDLs employs PCR-based sizing of repeats and sequencing approaches that identify length changes in repetitive regions, aiding studies of mutation processes and cancer diagnostics.