Journal: PLoS Genetics
Article Title: Viral Evasion of a Bacterial Suicide System by RNA-Based Molecular Mimicry Enables Infectious Altruism
Figure Lengend Snippet: Analysis of pseudo-ToxI as a potential antitoxin. (A) Alignment of the pseudo-ToxI and ToxI RNA sequences. Pseudo-ToxI nucleotides are coloured to match (B) and (C), with the green and purple bases denoting the 5′ and 3′ ends of a single pseudoknot, respectively. Mutated nucleotides in pseudo-ToxI are coloured orange and numbered according to their grouping, whilst the asterisk indicates the additional 3′ nucleotide. The dotted line connecting the U in group 3 indicates the uracil that is deleted in the case of expanded repeats with 2T sequences rather than 3T. (B) Schematic of the ToxI pseudoknot. Each position containing a mutation in the pseudo-ToxI RNA has been bracketed, with the ToxI base separated from the pseudo-ToxI base by a ‘/’. The mutations have been grouped 1–5, according to position, and highlighted in orange, with the 5′ and 3′ termini in green and violet, respectively. Indels, such as U17 that is deleted in some pseudo-ToxI repeats, and the additional A* inserted in all, have been bordered by a dashed line. Base interactions are indicated by black lines, and duplex and triplex base-interactions are bordered in grey. (C) Detail of the ToxIN trimer with each pseudoknot shown either in blue, purple or beige. Each ToxN monomer is shown as a grey surface. The blue pseudoknot is oriented relative to (B). The positions of mutation groups are shown, with the group number encircled in the same colour as the corresponding pseudoknot. The additional nucleotide of group 5 is not visible as this was not in the original solved ToxIN structure. PDB: 2XDB. (D) Pseudo-ToxI cannot protect from ToxN in an over-expression assay. Protection assays were conducted as per Materials and Methods using strains of E. coli DH5α carrying both pTA49 (inducible ToxN) and a second inducible antitoxin vector as shown, including use of pTA100 as a vector-only control, “vector”. Error bars indicate the standard deviation of triplicate data. (E) Protection assays using mutants of ToxI carried out as in (D) with the antitoxin mutations in each construct numbered as per (B). (F) Protection assays carried out as in (D), testing the full escape loci of ΦTE wt, ΦTE-A and ΦTE-F with full ToxI as a positive control. Under these conditions, there was sufficient antitoxin present to inhibit induced ToxN even without specific induction of the ToxI and ΦTE-F constructs.
Article Snippet: All experiments were performed with E. coli strain DH5α (Gibco/BRL) or Pectobacterium atrosepticum SCRI1043 and derivatives thereof.
Techniques: Mutagenesis, Over Expression, Plasmid Preparation, Standard Deviation, Construct, Positive Control