Paull T T, Haykinson M J, Johnson R C
Molecular Biology Institute, University of California Los Angeles 90024, USA.
Biochimie. 1994;76(10-11):992-1004. doi: 10.1016/0300-9084(94)90024-8.
The prokaryotic protein HU functions as an accessory factor in many different biochemical reactions. We have characterized the role of HU in assembling the invertasome, an intermediate nucleoprotein complex involved in Hin-mediated site-specific recombination. Formation of this complex requires the looping of intervening DNA segments between sites bound by the Hin recombinase and the Fis protein. HU stimulates this process on substrates containing intervening segments of length < 100 bp. Characterization of the activity of HU in Hin-mediated recombination in vitro and in vivo yields evidence that its role in this reaction is primarily to facilitate the looping of the intervening DNA segment. By using this reaction as an assay, we identify proteins from mammals, yeast, trypanosomes, and wheat which can fulfill the same function in vitro. Using ligase-mediated circularization of short DNA fragments we also show that HU, the high mobility group (HMG) 1 and 2 proteins from mammals, and a protein from yeast can bend DNA extremely efficiently. These results support the view that this ubiquitous class of proteins enhance the assembly of nucleoprotein complexes under conditions of limited DNA flexibility.
原核生物蛋白HU在许多不同的生化反应中作为辅助因子发挥作用。我们已经阐明了HU在组装转化体中的作用，转化体是一种参与Hin介导的位点特异性重组的中间核蛋白复合物。形成这种复合物需要在由Hin重组酶和Fis蛋白结合的位点之间的间隔DNA片段形成环。HU在含有长度<100 bp间隔片段的底物上刺激这一过程。对HU在体外和体内Hin介导的重组中的活性进行表征，结果表明其在该反应中的作用主要是促进间隔DNA片段的环化。通过使用该反应作为检测方法，我们鉴定出了来自哺乳动物、酵母、锥虫和小麦的能够在体外发挥相同功能的蛋白质。利用连接酶介导的短DNA片段环化，我们还表明HU、来自哺乳动物的高迁移率族（HMG）1和2蛋白以及来自酵母的一种蛋白能够极其有效地使DNA弯曲。这些结果支持了这样一种观点，即在DNA灵活性有限的条件下，这类普遍存在的蛋白质会增强核蛋白复合物的组装。
