PROMOTION OF PARALLEL DNA QUADRUPLEXES BY A YEAST TELOMERE BINDING-PROTEIN - A CIRCULAR-DICHROISM STUDY

Repressor-activator protein 1 (RAP1) has an essential role in the main tenance of yeast telomeres. Yeast telomeric DNA consists of simple rep eated G-rich sequences that are bound by RAP1. We have found that RAP1 , in addition to its known binding activity for double-stranded DNA, i nteracts with the G-rich strand containing guanine base (G)-tetrads. W e show here using circular dichroism spectroscopy that RAP1 promotes t he formation of one particular type of DNA quadruplex, parallel G4-DNA . Furthermore, RAP1 is able to bind to both preformed parallel and ant iparallel DNA quadruplexes. These results have implications for the po ssible use of DNA quadruplexes in telomere-telomere association in viv o.