Nucleic Acids Research, 2000, Vol. 28, No. 18 3642-3648
© 2000 Oxford University Press
Telomere repeat DNA forms a large non-covalent complex with unique cohesive properties which is dissociated by Werner syndrome DNA helicase in the presence of replication protein A
AGENE Research Institute, 200 Kajiwara, Kamakura, Kanagawa 247-0063, Japan and 1Department of Cellular and Molecular Biology, Hiroshima University School of Medicine, Minami-ku, Hiroshima 734-8551, Japan
We describe the unique structural features of a large telomere repeat DNA complex (TRDC) of >20 kb generated by a simple PCR using (TTAGGG)4 and (CCCTAA)4 as both primers and templates. Although large, as determined by conventional agarose gel electrophoresis, the TRDC was found to consist of short single-stranded DNA telomere repeat units of between several hundred and 3000 bases, indicating that it is a non-covalent complex comprising short cohesive telomere repeat units. S1 nuclease digestion showed that the TRDC contains both single- and double-stranded portions stable enough to survive glycerol density gradient centrifugation, precipitation with ethanol and gel electrophoresis. Sedimentation analysis suggests that a part of the TRDC is non-linear and consists of a three-dimensional network structure. After treatment with Werner DNA helicase the TRDC dissociated into smaller fragments, provided that human replication protein A was present, indicating that: (i) the TRDC is a new substrate for the Werner syndrome helicase; (ii) the telomere repeat sequence re-anneals rapidly unless unwound single-stranded regions are protected by replication protein A; (iii) the TRDC may provide a new clue to understanding deleterious telomeretotelomere interactions that can lead to genomic instability. Some properties of the TRDC account for the extra-chromosomal telomere repeat (ECTR) DNA that exists in telomerase-negative immortalized cell lines and may be involved in maintaining telomeres.
* To whom correspondence should be addressed. Tel: +81 467 46 4910; Fax: +81 467 48 6595; Email: furuichi@agene.co.jp
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