Structural basis of template-boundary definition in Tetrahymena telomerase.

Telomerase is required to maintain repetitive G-rich telomeric DNA sequences at chromosome ends. To do so, the telomerase reverse transcriptase (TERT) subunit reiteratively uses a small region of the integral telomerase RNA (TER) as a template. An essential feature of telomerase catalysis is the strict definition of the template boundary to determine the precise TER nucleotides to be reverse transcribed by TERT. We report the 3 Å crystal structure of the Tetrahymena TERT RNA binding domain (tTRBD) bound to the template boundary element (TBE) of TER. tTRBD is wedged into the base of the TBE RNA stem-loop and each of the flanking RNA strands wraps around opposite sides of the protein domain. The structure illustrates how the tTRBD establishes the template boundary by positioning the TBE the correct distance from the TERT active site to prohibit copying of non-template nucleotides.

端粒酶是维持染色体末端富含鸟嘌呤（G）的重复端粒DNA序列所必需的。为此，端粒酶逆转录酶（TERT）亚基反复使用完整的端粒酶RNA（TER）的一个小区域作为模板。端粒酶催化的一个重要特征是对模板边界的严格界定，以确定由TERT逆转录的精确TER核苷酸。我们报道了嗜热四膜虫TERT RNA结合结构域（tTRBD）与TER的模板边界元件（TBE）结合的3 Å晶体结构。tTRBD嵌入TBE RNA茎环的底部，两侧的RNA链分别环绕蛋白质结构域的相对两侧。该结构阐明了tTRBD如何通过将TBE定位在距TERT活性位点正确的距离来确定模板边界，从而阻止非模板核苷酸的复制。