Kim J H, Marshall A G
Department of Chemistry, Ohio State University, Columbus 43210.
Biochem Biophys Res Commun. 1990 Jun 29;169(3):1068-74. doi: 10.1016/0006-291x(90)92003-i.
A possible switch between two conformations, previously observed in an enzymatically cleaved fragment of E. coli 5S ribosomal RNA (a Gram-negative bacterium) containing helices II and III, has been examined by means of proton nuclear magnetic resonance spectroscopy (10-15 ppm) as a function of [Mg2+] and temperature for an RNase-T1 digested fragment of Bacillus megaterium 5S rRNA (a Gram-positive bacterium) containing the same helices II and III. The conformational changes induced in the fragment are not accompanied by breakage of some base-pairs and formation of others, but rather consist simply of tightening or loosening of helices with retention of existing base-pairs. Helix III is found to be more flexible than helix II. Finally, the loop conformation is conserved over a wide range of Mg2+ concentration, suggesting that the loop may serve an important role in the biological function of 5S rRNA in ribosomes.
大肠杆菌5S核糖体RNA（一种革兰氏阴性细菌）的酶切片段中曾观察到两种构象之间可能存在转换，该片段包含螺旋II和螺旋III。现已通过质子核磁共振波谱法（10 - 15 ppm），针对巨大芽孢杆菌5S rRNA（一种革兰氏阳性细菌）的RNase - T1消化片段，研究了作为[Mg2 +]和温度函数的相同螺旋II和螺旋III之间的构象转换。片段中诱导的构象变化并非伴随着一些碱基对的断裂和其他碱基对的形成，而仅仅是螺旋的收紧或松弛，同时保留现有的碱基对。发现螺旋III比螺旋II更具柔韧性。最后，环构象在很宽的Mg2 +浓度范围内保持不变，这表明该环可能在核糖体中5S rRNA的生物学功能中发挥重要作用。
