A Parallel G Quadruplex-Binding Protein Regulates the Boundaries of DNA Elimination Events of Tetrahymena thermophila

Guanine (g)-rich dna readily forms four-stranded quadruplexes in vitro,but evidence for their participation in genome regulation is limited. we have identified a quadruplex-binding protein,lia3,that controls the boundaries of germline-limited,internal eliminated sequences (iess) of tetrahymena thermophila. differentiation of this ciliate’s somatic genome requires excision of thousands of iess,targeted for removal by small-rna-directed heterochromatin formation. in cells lacking lia3 (δlia3),the excision of iess bounded by specific g-rich polypurine tracts was impaired and imprecise,whereas the removal of iess without such controlling sequences was unaffected. we found that oligonucleotides containing these polypurine tracts formed parallel g-quadruplex structures that are specifically bound by lia3. the discovery that lia3 binds g-quadruplex dna and controls the accuracy of dna elimination at loci with specific g-tracts uncovers an unrecognized potential of quadruplex structures to regulate chromosome organization. © 2016 carle et al.