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In eukaryotic DNA replication, a single-stranded DNA fragment remains at the end of a chromosome after the removal of the final primer. This section of DNA cannot be replicated in the same manner as the rest of the strand because there is no 3’ end to which the newly synthesized DNA can attach. This non-replicated fragment results in gradual loss of the chromosomal DNA during each cell duplication. Additionally, it can induce a DNA damage response by enzymes that recognize single-stranded...
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In eukaryotic cells, DNA replication is highly conserved and tightly regulated. Multiple linear chromosomes must be duplicated with high fidelity before cell division, so there are many proteins that fulfill specialized roles in the replication process. Replication occurs in three phases: initiation, elongation, and termination, and ends with two complete sets of chromosomes in the nucleus.
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Translesion (TLS) polymerases rescue stalled DNA polymerases at sites of damaged bases by replacing the replicative polymerase and installing a nucleotide across the damaged site. Doing so, TLS allows additional time for the cell to repair the damage before resuming regular DNA replication.
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DNA-binding determinants and cellular thresholds for human telomerase repeat addition processivity.

Robert Alexander Wu1, Jane Tam1, Kathleen Collins2

  • 1Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA.

The EMBO Journal
|May 13, 2017
PubMed
Summary
This summary is machine-generated.

Telomerase repeat addition processivity is crucial for telomere maintenance, but cells can tolerate lower levels. Altering telomerase expression impacts telomere length.

Keywords:
DNA–RNA duplexreverse transcriptasesingle‐stranded DNAtelomerasetelomere maintenance

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • The enzyme telomerase (reverse transcriptase) adds repetitive DNA sequences to the ends of chromosomes, counteracting the shortening that occurs during replication.
  • Telomere shortening is linked to cellular aging and disease, making telomerase activity a key area of research.
  • The processivity of telomerase, its ability to synthesize multiple repeats in one binding event, is thought to be critical but has not been fully understood in relation to disease.

Purpose of the Study:

  • To identify specific amino acid residues within the telomerase active site that regulate repeat addition processivity.
  • To investigate how these residues influence the enzyme's interaction with both single-stranded and double-stranded DNA.
  • To assess the cellular effects of altered telomerase processivity on telomere length maintenance and overall telomere biology.

Main Methods:

  • Biochemical assays were used to delineate active-site side chains critical for telomerase repeat addition processivity.
  • Studies examined the impact of these modifications on telomerase's handling of DNA substrates.
  • Cellular experiments tested the consequences of reduced or absent processivity on telomere maintenance.

Main Results:

  • Specific side chains in the telomerase active site were identified as key determinants of repeat addition processivity.
  • A new model for DNA and RNA handling during processive repeat synthesis was proposed based on biochemical findings.
  • While essential for function, telomere maintenance is possible with reduced telomerase processivity; however, overexpression of low-processivity telomerase leads to dramatic telomere elongation.

Conclusions:

  • Repeat addition processivity is essential for optimal telomerase function, but not strictly required for telomere maintenance.
  • Altering telomerase processivity has distinct effects on telomere length compared to changes in telomerase expression levels.
  • These findings provide new insights into the complex regulation of telomere length and offer potential therapeutic targets for telomere-related diseases.