Department of Microbiology and Immunology, College of Medicine, University of Saskatchewan, Academic Health Sciences Building, 107 Wiggins Rd, Saskatoon, SK S7N 5E5, Canada.
Nucleic Acids Res. 2013 Dec;41(22):10438-48. doi: 10.1093/nar/gkt832. Epub 2013 Sep 17.
Spirochetes of the genus Borrelia include the tick-transmitted causative agents of Lyme disease and relapsing fever. They possess unusual genomes composed mainly of linear replicons terminated by closed DNA hairpin telomeres. Hairpin telomeres present an uninterrupted DNA chain to the replication machinery overcoming the 'end-replication problem' for the linear replicons. Hairpin telomeres are formed from inverted repeat replicated telomere junctions by the telomere resolvase, ResT. ResT uses a reaction mechanism similar to that of the type IB topoisomerases and tyrosine recombinases. We report here that ResT also possesses single-strand annealing activity and a limited ability to promote DNA strand exchange reactions on partial duplex substrates. This combination of activities suggests ResT is a nexus between the seemingly distinct processes of telomere resolution and homologous recombination. Implications for hairpin telomere replication and linear plasmid recombination, including antigenic variation, are discussed.
螺旋体属的螺旋体包括蜱传莱姆病和回归热的致病因子。它们具有不寻常的基因组，主要由线性复制子组成，末端为闭合的 DNA 发夹端粒。发夹端粒为复制机制提供了一条不间断的 DNA 链，克服了线性复制子的“末端复制问题”。发夹端粒是由端粒解旋酶 ResT 复制的端粒重复序列的反向重复形成的。ResT 使用的反应机制类似于 I 型拓扑异构酶和酪氨酸重组酶。我们在这里报告，ResT 还具有单链退火活性和在部分双链底物上促进 DNA 链交换反应的有限能力。这些活性的结合表明，ResT 是端粒解决和同源重组这两个看似截然不同的过程之间的连接点。讨论了发夹端粒复制和线性质粒重组（包括抗原变异）的意义。
