Kim Min-Jung, Lee Yoo Kyung, Lee Hong Kum, Im Hana
Department of Molecular Biology, Sejong University, 98 Gunjadong, Kwangjin-gu, Seoul, 143-747, Korea.
Protein J. 2007 Jan;26(1):51-9. doi: 10.1007/s10930-006-9044-1.
Polar organisms should have mechanisms to survive the extremely cold environment. Four genes encoding cold-shock proteins, which are small, cold-induced bacterial proteins, have been cloned from the Antarctic bacterium Streptomyces sp. AA8321. Since the specific functions of any polar bacterial or Streptomyces cold-shock proteins have not yet been determined, we examined the role of cold-shock protein A from Streptomyces sp. AA8321 (CspA(St)). Gel filtration chromatography showed that purified CspA(St) exists as a homodimer under physiological conditions, and gel shift assays showed that it binds to single-stranded, but not double-stranded, DNA. Overexpression of CspA(St) in Escherichia coli severely impaired the ability of the host cells to form colonies, and the cells developed an elongated morphology. Incorporation of a deoxynucleoside analogue, 5-bromo-2'-deoxyuridine, into newly synthesized DNA was also drastically diminished in CspA(St)-overexpressing cells. These results suggest that CspA(St) play a role in inhibition of DNA replication during cold-adaptation.
极地生物应该具备在极端寒冷环境中生存的机制。从南极细菌链霉菌属菌株AA8321中克隆出了四个编码冷休克蛋白的基因，冷休克蛋白是一类小型的、受寒冷诱导的细菌蛋白。由于尚未确定任何极地细菌或链霉菌冷休克蛋白的具体功能，我们研究了链霉菌属菌株AA8321的冷休克蛋白A（CspA(St)）的作用。凝胶过滤色谱分析表明，纯化后的CspA(St)在生理条件下以同型二聚体形式存在，凝胶迁移试验表明它能与单链DNA结合，但不能与双链DNA结合。在大肠杆菌中过表达CspA(St)会严重损害宿主细胞形成菌落的能力，并且细胞会呈现出细长的形态。在过表达CspA(St)的细胞中，脱氧核苷类似物5-溴-2'-脱氧尿苷掺入新合成DNA的过程也大幅减少。这些结果表明，CspA(St)在冷适应过程中对DNA复制的抑制发挥作用。
