Attempted use of PACE for riboswitch discovery generates three new translational theophylline riboswitch side products.

OBJECTIVE: The purpose of this project was to use an in vivo method to discover riboswitches that are activated by new ligands. We employed phage-assisted continuous evolution (PACE) to evolve new riboswitches in vivo. We started with one translational riboswitch and one transcriptional riboswitch, both of which were activated by theophylline. We used xanthine as the new target ligand during positive selection followed by negative selection using theophylline. The goal was to generate very large M13 phage populations that contained unknown mutations, some of which would result in new aptamer specificity. We discovered side products of three new theophylline translational riboswitches with different levels of protein production. RESULTS: We used next generation sequencing to identify M13 phage that carried riboswitch mutations. We cloned and characterized the most abundant riboswitch mutants and discovered three variants that produce different levels of translational output while retaining their theophylline specificity. Although we were unable to demonstrate evolution of new riboswitch ligand specificity using PACE, we recommend careful design of recombinant M13 phage to avoid evolution of "cheaters" that short circuit the intended selection pressure.

In Situ Dark Adaptation Enhances the Efficiency of DNA Extraction from Mature Pin Oak (Quercus palustris) Leaves, Facilitating the Identification of Partial Sequences of the 18S rRNA and Isoprene Synthase (IspS) Genes.

Mature oak (Quercus spp.) leaves, although abundantly available during the plants' developmental cycle, are rarely exploited as viable sources of genomic DNA. These leaves are rich in metabolites difficult to remove during standard DNA purification, interfering with downstream molecular genetics applications. The current work assessed whether in situ dark adaptation, to deplete sugar reserves and inhibit secondary metabolite synthesis could compensate for the difficulties encountered when isolating DNA from mature leaves rich in secondary metabolites. We optimized a rapid, commercial kit based method to extract genomic DNA from dark- and light-adapted leaves. We demonstrated that in situ dark adaptation increases the yield and quality of genomic DNA obtained from mature oak leaves, yielding templates of sufficiently high quality for direct downstream applications, such as PCR amplification and gene identification. The quality of templates isolated from dark-adapted pin oak leaves particularly improved the amplification of larger fragments in our experiments. From DNA extracts prepared with our optimized method, we identified for the first time partial segments of the genes encoding 18S rRNA and isoprene synthase (IspS) from pin oak (Quercus palustris), whose full genome has not yet been sequenced.