The staphylococcal plasmid phi 11de is capable of transduction in the absence of both a helper bacteriophage and detectable plaque-forming bacteriophage. The mechanism of transfer is distinct from generalized transduction in that it does not transduce chromosomal material and is selective with respect to the plasmid DNA that is transduced. The transductants containing phi 11de have the following characteristics: (i) erythromycin resistance at levels displayed by the donor, (ii) expression of and susceptibility to plasmid incompatibility, (iii) dependence upon the host recombination system during transduction, (iv) complementation of phi 11 mutants, and (v) reactivation of UV-irradiated phage.

Transduction of plasmid pC194 and bacteriophage 4llde varied inversely with the multiplicity of infection. As the multiplicity of infection decreased from 10-' to 10-5 PFU/CFU, the transduction frequency of pC194 increased 104-fold; the transduction frequency of 4llde increased 300-fold with a 100-fold decrease in multiplicity of infection. Physical and genetic analysis of the transduced DNA showed that pC194 resided in the phage particle as a random, circularly permuted linear concatemer. In DNA prepared from phage that cotransduced pC194 and 411de, pC194 resided in the transducing phage primarily as a linear multimer of 15.8 kilobases, or about 5.4 pC194 monomers. The pC194 multimer was randomly inserted into the 411 genome.Small staphylococcal plasmids are not transduced by generalized transduction, as are chromosomal determinants (2,27). This was first shown by Grubb et al. (6,7), who demonstrated cotransduction of staphylococcal streptomycin resistance and tetracycline resistance plasmids. Later, Stiffler et al. (26) and Iordanescu (10) extended this observation to include a variety of other small plasmids. These investigations highlight a dilemma that arises because cotransduction of plasmid DNA in Staphylococcus spp. often occurs at frequencies higher than predicted for a random packaging model. Transduction of a single plasmid species occurs at frequencies of about 10-5 to 10-8 per PFU; frequencies vary depending upon the plasmid used and the transducing phage (2). Other unselected plasmids are often cotransduced at between 1 and 10% of the single transduction frequency (9), even though the predicted cotransduction rates for randomly packaged plasmids should be the product of the probabilities of the single transductional events. This high rate leads to the suggestion that cotransducing plasmids are not randomly assorted, but associate in some specific way. Iordanescu (10) suggested that some staphylococcal plasmids become transiently associated during the formation of the transducing particle. Furthermore, this transient association is limited to specific pairs that share short regions of homology (14). Cotransduced plasmids generally resolve into individual replicons in the recipient cell, but occasionally (ca. 1%) the plasmid phenotypes remain associated as stable plasmid cointegrates that arise from site-and orientation-specific recombination (14). Plasmid cointegrates are stable in subsequent transductions or transformations and do not under normal circumstances dissociate into the component replicons (9).Examination of these transient transductional associations has been complicated by the assumption that these events occur at relatively low frequencies in a transducing phage population. However, we have utilized the finding that plasmid transduction occurs at higher rates at very low multiplicity of infection (MOI) (19,20) to directly analyze the transducing DNA in the phage particles. * Corresponding author. t Contribution no. 85-82-J from the Kansas Agricultural Experiment Station, Manhattan. t ...

Background: Biomarker detection strategies have, in recent years, been moving towards nucleic acid-based detection systems in the form of aptamers, short oligonucleotide sequences which have shown promise in pre-clinical and research settings. One such aptamer is M5-15, a DNA aptamer raised against human alpha synuclein (α-syn) the causative agent in Lewy body and Parkinson's disease (PD) associated dementia. While this aptamer has shown promise, in silico methodologies have demonstrated a capacity to produce aptamers that have higher affinities for their targets than in vitro generated sequences. Methods: A Python script random generated library of DNA sequences were screened based on their thermodynamic stability with the use of DINAMelt server-QuickFold web server. The selected sequences were examined with MFold in order to generate secondary structure data that were used to produce 3D data with the use of RNA composer software. Further on, the structure was corrected and RNA was replaced with DNA and the virtual screening for α-syn aptamer took place with a series of molecular docking experiments with the use of CSD-Discovery-GOLD software. Results: Herein we propose an alternative in silico generated aptamer we call TMG-79 which demonstrates greater affinity for the target compared to M5-15 (M5-15 = -15.9 kcal/mol, TMG-79 = -17.77 kcal/mol) as well as better ChemPLP fitness scoring between the top poses . Structural analysis suggests that while there are similarities, the greater potential flexibility of TMG-79 could be promoting greater affinity for the α-syn compared to M5-15. Conclusions: In silico methods of aptamer generation has the potential to revolutionise the field of aptamer design. We feel that further development of TMG-79 and validation in vitro will make it a viable candidate for diagnostic and research use in the future.