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Protein Binding to Expanded Telomere Repeats in Tetrahymena thermophila
Author(s) -
MCGUIRE JENNIFER M.,
GANA JOYCE ACHE,
PETCHERSKAIA MARINA,
KIRK KAREN E.
Publication year - 2003
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.2003.tb00146.x
Subject(s) - tetrahymena , biology , telomere , dna , thymine , guanine , telomere binding protein , binding site , microbiology and biotechnology , repeated sequence , genetics , dna binding protein , nucleotide , gene , transcription factor , genome
. The ends of eukaryotic chromosomes are protected by DNA‐protein structures called telomeres. Telomeric DNA is highly conserved, usually consisting of long tracts of a repeating G‐rich sequence. Tetrahymena thermophila telomeric DNA consists of alternating blocks of GGGG and TT sequences (i.e. a G4T2 repeat sequence). We examined the relative importance of the guanine and thymine elements of the repeat sequence in promoting in vitro binding by T. thermophila proteins. We identified single‐ and, for the first time, double‐stranded telomere binding activities from a crude T. thermophila protein extract and tested the binding of these activities to altered telomere repeat sequences. All deletions or substitutions made to the guanine element virtually abolished binding, indicating that four G's are essential for recognition by the binding activity. However, G's alone are not sufficient for efficient binding, as elimination of the thymine element dramatically reduced binding. By contrast, substantial expansion of the thymine element was well tolerated, even though one such change, G4T4, is lethal in vivo. We tested up to a four‐fold expansion of the thymine element and found that highly efficient binding was still achieved. These results suggest a minimal recognition sequence for T. thermophila proteins, with the T element providing an important spacer between essential G elements. demonstrate some flexibility in the binding of many telomere proteins, because the variant sequences tested often contain more than one base change, the minimal changes that permit or disrupt binding cannot be deduced.