Yu Yuen-Tsu N, Cooper Elizabeth, Velicer Gregory J
Institute of Integrative Biology, ETH Zurich, Universitätstrasse 16, 8092, Zurich, Switzerland.
Department of Biology, Indiana University, Bloomington, IN, 47405, USA.
Sci Rep. 2017 Nov 13;7(1):15411. doi: 10.1038/s41598-017-15439-w.
The small RNA (sRNA) Pxr negatively controls multicellular fruiting body formation in the bacterium Myxococcus xanthus, inhibiting the transition from growth to development when nutrients are abundant. Like many other prokaryotic sRNAs, Pxr is predicted to fold into three stem loops (SL1-SL3). SL1 and SL2 are highly conserved across the myxobacteria, whereas SL3 is much more variable. SL1 is necessary for the regulatory function of Pxr but the importance of SL3 in this regard is unknown. To test for cis genetic elements required for Pxr function, we deleted the entire pxr gene from a developmentally defective strain that fails to remove Pxr-mediated blockage of development and reintroduced variably truncated fragments of the pxr region to test for their ability to block development. These truncations demonstrated that SL3 is necessary for Pxr function in the defective strain. We further show that a highly conserved eight-base-pair segment of SL3 is not only necessary for Pxr to block development in the defective strain under starvation conditions, but is also required for Pxr to prevent fruiting body development by a developmentally proficient wild-type strain under high-nutrient conditions. This conserved segment of SL3 is also necessary for detectable levels of Pxr to accumulate, suggesting that this segment either stabilizes Pxr against premature degradation during vegetative growth or positively regulates its transcription.
小RNA（sRNA）Pxr对粘球菌的多细胞子实体形成起负调控作用，在营养丰富时抑制从生长到发育的转变。与许多其他原核sRNA一样，Pxr预计会折叠成三个茎环（SL1 - SL3）。SL1和SL2在粘细菌中高度保守，而SL3的变化则大得多。SL1是Pxr调控功能所必需的，但SL3在这方面的重要性尚不清楚。为了测试Pxr功能所需的顺式遗传元件，我们从一个发育缺陷型菌株中删除了整个pxr基因，该菌株无法消除Pxr介导的发育阻滞，然后重新引入pxr区域的可变截短片段，以测试它们阻断发育的能力。这些截短表明SL3对于缺陷型菌株中Pxr的功能是必需的。我们进一步表明，SL3的一个高度保守的八碱基对片段不仅是Pxr在饥饿条件下阻断缺陷型菌株发育所必需的，也是Pxr在高营养条件下阻止发育良好的野生型菌株形成子实体所必需的。SL3的这个保守片段对于可检测水平的Pxr积累也是必需的，这表明该片段要么在营养生长期间稳定Pxr以防止其过早降解，要么正向调节其转录。
