Andrew F Brown

Publications (2)17.9 Total impact

• Article: RNA/DNA hybrid binding affinity determines telomerase template-translocation efficiency.

  Xiaodong Qi, Mingyi Xie, Andrew F Brown, Christopher J Bley, Joshua D Podlevsky, Julian J-L Chen
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  ABSTRACT: Telomerase synthesizes telomeric DNA repeats onto chromosome termini from an intrinsic RNA template. The processive synthesis of DNA repeats relies on a unique, yet poorly understood, mechanism whereby the telomerase RNA template translocates and realigns with the DNA primer after synthesizing each repeat. Here, we provide evidence that binding of the realigned RNA/DNA hybrid by the active site is an essential step for template translocation. Employing a template-free human telomerase system, we demonstrate that the telomerase active site directly binds to RNA/DNA hybrid substrates for DNA polymerization. In telomerase processivity mutants, the template-translocation efficiency correlates with the affinity for the RNA/DNA hybrid substrate. Furthermore, the active site is unoccupied during template translocation as a 5 bp extrinsic RNA/DNA hybrid effectively reduces the processivity of the template-containing telomerase. This suggests that strand separation and template realignment occur outside the active site, preceding the binding of realigned hybrid to the active site. Our results provide new insights into the ancient RNA/DNA hybrid binding ability of telomerase and its role in template translocation.
  The EMBO Journal 01/2012; 31(1):150-61. · 9.20 Impact Factor
• Source

  Available from: Julian J-L Chen

  Article: Ancestral mutation in telomerase causes defects in repeat addition processivity and manifests as familial pulmonary fibrosis.

  Jonathan K Alder, Joy D Cogan, Andrew F Brown, Collin J Anderson, William E Lawson, Peter M Lansdorp, John A Phillips, James E Loyd, Julian J-L Chen, Mary Armanios
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  ABSTRACT: The telomerase reverse transcriptase synthesizes new telomeres onto chromosome ends by copying from a short template within its integral RNA component. During telomere synthesis, telomerase adds multiple short DNA repeats successively, a property known as repeat addition processivity. However, the consequences of defects in processivity on telomere length maintenance are not fully known. Germline mutations in telomerase cause haploinsufficiency in syndromes of telomere shortening, which most commonly manifest in the age-related disease idiopathic pulmonary fibrosis. We identified two pulmonary fibrosis families that share two non-synonymous substitutions in the catalytic domain of the telomerase reverse transcriptase gene hTERT: V791I and V867M. The two variants fell on the same hTERT allele and were associated with telomere shortening. Genealogy suggested that the pedigrees shared a single ancestor from the nineteenth century, and genetic studies confirmed the two families had a common founder. Functional studies indicated that, although the double mutant did not dramatically affect first repeat addition, hTERT V791I-V867M showed severe defects in telomere repeat addition processivity in vitro. Our data identify an ancestral mutation in telomerase with a novel loss-of-function mechanism. They indicate that telomere repeat addition processivity is a critical determinant of telomere length and telomere-mediated disease.
  PLoS Genetics 03/2011; 7(3):e1001352. · 8.69 Impact Factor