Li Baomin, Reddy Sita, Comai Lucio
Department of Molecular Microbiology and Immunology, Institute for Genetic Medicine, University of Southern California, Los Angeles, CA 90033, USA.
Aging (Albany NY). 2009 Mar 17;1(3):289-302. doi: 10.18632/aging.100032.
Werner syndrome is a premature aging disease caused by loss of function mutations in the Werner syndrome protein (WRN) gene. WRN is a RecQ helicase that in contrast to every other member of this family of proteins possesses an exonuclease activity. The findings that cells lacking WRN activity display accelerated telomere shortening and WRN can be detected at chromosome ends suggest that this protein participates in some aspects of telomere metabolism. In this study we examined the impact of WRN on telomeric substrates with a 3' single-stranded overhang in vitro and show that WRN has sequence-specific exonuclease activity that removes several nucleotides inward with a periodical pattern from the 3' end of the telomeric overhang. This activity is strictly dependent on the presence of telomeric sequences in both the duplex DNA and 3' overhang DNA segment and is strongly inhibited by the telomeric factor POT1 but not TRF2. These data demonstrate that WRN processes telomeric DNA substrates with a 3' single-stranded overhang with high specificity and suggest that this protein could influence the configuration of telomere ends prior to the formation of a protective t-loop structure.
沃纳综合征是一种由沃纳综合征蛋白（WRN）基因功能丧失突变引起的早衰疾病。WRN是一种RecQ解旋酶，与该蛋白家族的其他成员不同，它具有核酸外切酶活性。缺乏WRN活性的细胞表现出端粒加速缩短，并且在染色体末端可检测到WRN，这些发现表明该蛋白参与端粒代谢的某些方面。在本研究中，我们在体外研究了WRN对具有3'单链突出端的端粒底物的影响，结果表明WRN具有序列特异性核酸外切酶活性，可从端粒突出端的3'端以周期性模式向内去除几个核苷酸。该活性严格依赖于双链DNA和3'突出端DNA片段中端粒序列的存在，并受到端粒因子POT1的强烈抑制，但不受TRF2的抑制。这些数据表明，WRN以高度特异性处理具有3'单链突出端的端粒DNA底物，并表明该蛋白可能在保护性t环结构形成之前影响端粒末端的构型。
