Identification of two human nuclear proteins that recognise the cytosine-rich strand of human telomeres in vitro |
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| Authors: | Lacroix L Liénard H Labourier E Djavaheri-Mergny M Lacoste J Leffers H Tazi J Hélène C Mergny J L |
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| Affiliation: | Laurent Lacroix, Hélène Liénard, Emmanuel Labourier, Mojgan Djavaheri-Mergny, Jérôme Lacoste, Henrik Leffers, Jamal Tazi, Claude Hélène, and Jean-Louis Mergny |
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| Abstract: | Most studies on the structure of DNA in telomeres have been dedicated to the double-stranded region or the guanosine-rich strand and consequently little is known about the factors that may bind to the telomere cytosine-rich (C-rich) strand. This led us to investigate whether proteins exist that can recognise C-rich sequences. We have isolated several nuclear factors from human cell extracts that specifically bind the C-rich strand of vertebrate telomeres [namely a d(CCCTAA)n repeat] with high affinity and bind double-stranded telomeric DNA with a 100× reduced affinity. A biochemical assay allowed us to characterise four proteins of apparent molecular weights 66–64, 45 and 35 kDa, respectively. To identify these polypeptides we screened a λgt11-based cDNA expression library, obtained from human HeLa cells using a radiolabelled telomeric oligonucleotide as a probe. Two clones were purified and sequenced: the first corresponded to the hnRNP K protein and the second to the ASF/SF2 splicing factor. Confirmation of the screening results was obtained with recombinant proteins, both of which bind to the human telomeric C-rich strand in vitro. |
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