Role of plasmids

Role of Plasmids in Evolution of O Antigen gene Clusters... 

From the population studies, several microbial isolates were selected to delineate the role of plasmids in enhanced biodegradation. A modification of the Birnboim and Doly (45) procedure was used to extract and demonstrate the presence of plasmid DNA in a Flavobacterium sp. (VI.15). A differential medium with 70 mg/L of yeast extract was developed to distinguish between butylate-degraders (But ) and isolates unable to utilize... 

What I hope to do in this paper is to give the reader a brief introduction to bacterial genetics and then to describe the research that has demonstrated the involvement of plasmids in carrying genes which encode enzymes that degrade pesticides. I will then discuss the possible role of plasmids in the development of the enhanced degradation phenomenon and the types of research that may lead to the delineation of the molecular events that lead to the development of rapid pesticide degradation in soils. 

Role of Plasmids Involved in Acetic Acid Resistance... 

Identification of proteins that bind to Z-DNA added one further step to the establishment of the presence of Z-DNA in vivo and its possible biological role. Herbert and Rich [22] demonstrated an in vitro assay system where one type of double-stranded RNA adenosine deaminase, called DRAD-binding Z-DNA. There are evidences that topoisomerase II from Drosophila, hiunan and calf thymus recognizes a number of DNA shapes, including Z-DNA [34,35]. Bloomfield and coworkers [36] have found that the condensation of plasmids is enhanced by Z-DNA conformation in d(CG)n repeats. The information related to B-Z transition [31], the effect of ligands on it [28,29] and X-ray crystal structure data [37,38] appear to suggest that the possible biological role of this polymorphic form of DNA will be soon established. 

The formation of three-stranded nucleic acid complexes was first demonstrated over five decades ago [56] but the possible biological role of an extended triplex was expanded by the discovery of the H-DNA structure in natural DNA samples [57-59]. H-DNA is an intermolecular triplex that is generally of the pyrimidine-purine x pyrimidine type ( dot -Watson-Crick pairing and cross Hoogsteen base paring) and can be formed at mirror repeat sequences in supercoiled plasmids [59]. 

Different approaches have been used to probe the role of chemokines and their receptors in experimental models of arthritis for instance, peptide antagonists or immunization of the host to promote the generation of endogenous neutralizing Abs via the use of chemokine plasmid DNA vaccination (Table 4 and Ref. 50), injection of neutralizing antibodies (Table 5), or mice that lack specific chemokine or chemokine receptors (Table 6). 

The mechanism of tellurium resistance has been investigated using genetic manipulation similar to that of Se (see above) and cellular oxidant capacity apparently plays an important role.144,206 A few tellurite determinants - both chromosomal and plasmid encoded - have been identified in bacte-ria.113,147 192 207 208 Recent studies have focused on the role of methyltransf-erases in Te resistance. Liu et a/.111 determined that the E. coli gene tehB uses S-adenosyl methionine and a methyltransferase in tellurite detoxification, but while no methylated tellurium compounds (see below) were observed, a loss of tellurite was observed in tellurite-amended cultures and Te complexation was inferred.191... 

In the absence of conclusive data on the role of a positive supercoiling wave, static positive supercoiling elicited by nucleosome reconstitution on relaxed or slightly positively-supercoiled plasmids [51] or by ethidium bromide intercalation in the loop of mononucleosomes on DNA minicircles [52] did not succeed either in releasing dimers. Moreover, circular dichroism, histone chemical modi-flcation and H3-thiol accessibility failed to detect an even slight alteration in the structure of such torsionally-stressed nucleosomes [51]. The reason was later found to lie in the ability of nucleosome entry/exit DNAs to form a positive crossing [52]. 

While isolation of a specific inhibitor will be necessary to assess the definitive role of the cytosolic nuclease in the low transfection efficiency in vivo, circumstantial evidence suggests that the metabolic instability of plasmid DNA represents one of the cellular barriers to gene transfer. Microinjection of DNA complexes with PEI has augmented the transfection efficiency (Pollard et al., 1998). Although the stability of the PEI-complexed DNA has not been determined in vivo, it has been demonstrated that the nuclease resistance of plasmid DNA is dramatically increased upon complex formation in vitro (Cappaccioli et al., 1993 Chiou et al., 1994 Thierry et al., 1997). Therefore, it is conceivable that faster diffusional mobility and decreased nuclease susceptibility jointly lead to the enhanced nuclear targeting efficiency of the PEI-condensed plasmid DNA. 

Iwasaki, A., Torres, C.A.T., Ohashi, P.S., Robinson, H.L. and Barber, B.H. (1997) The dominant role of bone marrow-derived cells in CTL induction following plasmid DNA immunization at different sites. J. Immunol., 159,11-14. 

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