ИСТИНА

Est3p is a component of telomerase complex which plays a fundamental role in genome maintenance, adding back the telomeric DNA repeats lost from chromosome ends. yeast telomerase complex contains the reverse transcriptase subunit Est2p, telomerase RNA TLC1, and additional components including Est1p and Est3p which have been proposed to play essential regulatory roles in vivo1. We have found that isolated Est3p binds G-quadruplexes in its GTP- but not GDP-form. The presence of G-quadruplex inhibits GTP hydrolysis. Mutant D86A Est3p lacks GTPase activity and binds G-quadruplexes regardless of the presence of GTP or GDP. Kinetic measurements of GTPase activity, EMSA, DMS probing of DNA structure were used to prove these findings. We propose that Est3p can be a part of the protein system in yeast similar to TEBPα-TEBPβ in ciliates2.