Pxr sRNA | |
---|---|
Identifiers | |
Symbol | Pxr |
Rfam | RF01812 |
Other data | |
RNA type | sRNA |
Domain(s) | Myxococcus xanthus, Stigmatella aurantiaca |
PDB structures | PDBe |
Pxr sRNA is a regulatory RNA which downregulates genes responsible for the formation of fruiting bodies in Myxococcus xanthus.[1] Fruiting bodies are aggregations of myxobacteria formed when nutrients are scarce,[2] the fruiting bodies permit a small number of the aggregated colony to transform into stress-resistant spores.[3]
Pxr exists in two forms: Pxr-L (a long form) and Pxr-S which is shorter. The short form was found to be expressed in cells during growth but is rapidly repressed during starvation. This finding implies that Pxr-S is specifically responsible for inhibiting the fruiting body development during cell growth when nutrients are abundant.[1]
Pxr homologs have only been found in one other taxon, namely Stigmatella aurantiaca. Homologs were not found in any other myxobacteria (such as Sorangium cellulosum[4] or Anaeromyxobacter dehalogenans[5]) which suggests the Pxr RNA gene may have a recent evolutionary origin in the sub-clade Myxococcales.[1]
PxR sRNA folds into 3 steam loops. SL1 and SL 2 are highly conserved across mycobacteria and SL1 is necessary for the regulatory function. However, a conserved eight-base-pair segment of the variable SL3 is necessary for PxR accumulation and multicellular development.[6]
Several mutations in the Pxr sRNA gene have been observed.[7] The first mutation causes an obligate cheat (OC) phenotype to emerge, these bacteria exploit the fruiting bodies of wild-type M. xanthus to sporulate more efficiently. This phenotype is thought to be caused by a mutation which prevents the repression of Pxr-S, thereby inhibiting the formation of fruiting bodies indefinitely. If Pxr-S is derived from Pxr-L, it may be that RNAi-like processing elements have been knocked out.[1]
In a laboratory experiment, the OC phenotype out-competed and excluded the wild type, eventually bringing about a population crash when there were not enough wild type bacteria to exploit.[7] After this event, a new phenotype emerged via spontaneous mutation dubbed phoenix (PX).[1] The PX phenotype was developmentally superior to both OC and wt, it was able to sporulate autonomously - without forming fruiting bodies and with high efficiency.[7] Two-component system operon (histidine kinase gene and a σ54 response regulator) is associated with production and processing of Pxr sRNA.[8]