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Efficient bacterial transcription of DNA nanocircle vectors with optimized single-stranded promoters.

ABSTRACT: We describe experiments aimed at establishing whether circular single-stranded DNAs can form promoters for bacterial transcription from small folded motifs. In vitro selection experiments were carried out on circular 103-nt DNA libraries encoding 40-nt randomized sequences as well as self-processing hammerhead ribozymes. Rounds of rolling circle transcription, reverse transcription-PCR, and recyclization were carried out to optimize transcription efficiency. Sequences were identified that are 80-fold more actively transcribed than the initial library by E. coli RNA polymerase (RNAP). The selected motifs were found to be more active than canonical E. coli promoters in the same context. Experiments also demonstrated that a single-stranded pseudopromoter identified by this selection can be transplanted to other circular DNA contexts and retain transcriptional activity. Results suggest that the promoter is localized in a short ( approximately 40 nt) hairpin, which is smaller than canonical E. coli promoters. To test whether this pseudopromoter was active in bacterial cells, a synthetic DNA nanocircle vector encoding a ribozyme targeted to a site in the marA drug resistance gene was constructed to contain an optimized single-stranded promoter. It is shown that this DNA circle can act as a "Trojan horse" in E. coli, being actively transcribed by the cellular RNAP and producing ribozymes that cleave a sequence in the marA drug resistance gene. The use of optimized single-stranded promoters in combination with synthetic nanocircle DNA vectors represents a potentially useful way to engender the synthesis of biologically active RNAs in living cells.

SUBMITTER: Ohmichi T

PROVIDER: S-EPMC117513 | biostudies-literature | 2002 Jan

REPOSITORIES: biostudies-literature

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Efficient bacterial transcription of DNA nanocircle vectors with optimized single-stranded promoters.

Ohmichi Tatsuo T Maki Angele A Kool Eric T ET

Proceedings of the National Academy of Sciences of the United States of America 20011218 1

We describe experiments aimed at establishing whether circular single-stranded DNAs can form promoters for bacterial transcription from small folded motifs. In vitro selection experiments were carried out on circular 103-nt DNA libraries encoding 40-nt randomized sequences as well as self-processing hammerhead ribozymes. Rounds of rolling circle transcription, reverse transcription-PCR, and recyclization were carried out to optimize transcription efficiency. Sequences were identified that are 80 ...[more]

PMID: 11752404

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Project description:Soils impact global carbon cycling and their resident microbes are critical to their biogeochemical processing and ecosystem outputs. Based on studies in marine systems, viruses infecting soil microbes likely modulate host activities via mortality, horizontal gene transfer, and metabolic control. However, their roles remain largely unexplored due to technical challenges with separating, isolating, and extracting DNA from viruses in soils. Some of these challenges have been overcome by using whole genome amplification methods and while these have allowed insights into the identities of soil viruses and their genomes, their inherit biases have prevented meaningful ecological interpretations. Here we experimentally optimized steps for generating quantitatively-amplified viral metagenomes to better capture both ssDNA and dsDNA viruses across three distinct soil habitats along a permafrost thaw gradient. First, we assessed differing DNA extraction methods (PowerSoil, Wizard mini columns, and cetyl trimethylammonium bromide) for quantity and quality of viral DNA. This established PowerSoil as best for yield and quality of DNA from our samples, though ∼1/3 of the viral populations captured by each extraction kit were unique, suggesting appreciable differential biases among DNA extraction kits. Second, we evaluated the impact of purifying viral particles after resuspension (by cesium chloride gradients; CsCl) and of viral lysis method (heat vs bead-beating) on the resultant viromes. DNA yields after CsCl particle-purification were largely non-detectable, while unpurified samples yielded 1-2-fold more DNA after lysis by heat than by bead-beating. Virome quality was assessed by the number and size of metagenome-assembled viral contigs, which showed no increase after CsCl-purification, but did from heat lysis relative to bead-beating. We also evaluated sample preparation protocols for ssDNA virus recovery. In both CsCl-purified and non-purified samples, ssDNA viruses were successfully recovered by using the Accel-NGS 1S Plus Library Kit. While ssDNA viruses were identified in all three soil types, none were identified in the samples that used bead-beating, suggesting this lysis method may impact recovery. Further, 13 ssDNA vOTUs were identified compared to 582 dsDNA vOTUs, and the ssDNA vOTUs only accounted for ∼4% of the assembled reads, implying dsDNA viruses were dominant in these samples. This optimized approach was combined with the previously published viral resuspension protocol into a sample-to-virome protocol for soils now available at protocols.io, where community feedback creates 'living' protocols. This collective approach will be particularly valuable given the high physicochemical variability of soils, which will may require considerable soil type-specific optimization. This optimized protocol provides a starting place for developing quantitatively-amplified viromic datasets and will help enable viral ecogenomic studies on organic-rich soils.

Dataset Information

Efficient bacterial transcription of DNA nanocircle vectors with optimized single-stranded promoters.

Publications

Efficient bacterial transcription of DNA nanocircle vectors with optimized single-stranded promoters.

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