Yu G L, Blackburn E H
Department of Microbiology and Immunology, University of California, San Francisco 94143.
Cell. 1991 Nov 15;67(4):823-32. doi: 10.1016/0092-8674(91)90077-c.
Healing of a broken chromosome and in eukaryotes involves acquisition of a telomere. During macronuclear development in ciliated protozoans, germline chromosomes are fragmented into linear subchromosomes, whose ends are healed by de novo addition of telomeres. We showed previously that the ribonucleoprotein enzyme telomerase elongates preexisting telomeres by synthesizing one telomeric DNA strand, using a template sequence in the RNA moiety of the enzyme. By marking telomerase with a mutation in the telomerase RNA template, which causes synthesis of novel telomeric sequences, we now show that in the ciliate Tetrahymena, telomerase directly adds telomeric DNA onto nontelomeric sequences during developmentally controlled chromosome healing. Unexpectedly, one telomerase RNA template mutation converted telomerase from an enzyme that normally synthesizes precisely templated sequences to a less precise polymerase that sometimes synthesizes irregular telomeric repeats in vivo.
在真核生物中，断裂染色体的修复涉及端粒的获得。在纤毛原生动物的大核发育过程中，生殖系染色体被断裂成线性亚染色体，其末端通过端粒的从头添加而修复。我们之前表明，核糖核蛋白酶端粒酶通过使用该酶RNA部分中的模板序列合成一条端粒DNA链来延长预先存在的端粒。通过用端粒酶RNA模板中的突变标记端粒酶，该突变导致新的端粒序列的合成，我们现在表明，在纤毛虫四膜虫中，端粒酶在发育控制的染色体修复过程中直接将端粒DNA添加到非端粒序列上。出乎意料的是，一种端粒酶RNA模板突变将端粒酶从一种通常合成精确模板化序列的酶转变为一种不太精确的聚合酶，该聚合酶有时在体内合成不规则的端粒重复序列。
