Label-free DNA electrochemical sensor based on a PNA-functionalized conductive polymer.

An electrochemical hybridization biosensor based on peptide nucleic acid (PNA) probe is presented. PNA were attached covalently onto a quinone-based electroactive polymer. Changes in flexibility of the PNA probe strand upon hybridization generates electrochemical changes at the polymer-solution interface. A reagentless and direct electrochemical detection was obtained by detection of the electrochemical changes using square wave voltammetry (SWV). An increase in the peak current of quinone was observed upon hybridization of probe on the target, whereas no change is observed with non-complementary sequence. In addition, the biosensor is highly selective to effectively discriminate a single mismatch on the target sequence. The sensitivity is also presented and discussed.

Location of F plasmid transfer operon genes traC and traW and identification of the traW product.

As part of an analysis of the conjugative transfer genes associated with the expression of F pili by plasmid F, we have investigated the physical location of the traC and traW genes. We found that plasmid clones carrying a 2.95-kilobase EcoRI-EcoRV F transfer operon fragment were able to complement transfer of F lac traC mutants and expressed an approximately 92,000-dalton product that comigrates with TraC. We also found that traW-complementing activity was expressed from plasmids carrying a 900-base-pair SmaI-HincII fragment. The traW product was identified as an approximately 23,000-dalton protein. The two different F DNA fragments that expressed traC and traW activities do not overlap. Our data indicate that the traC gene is located in a more-tra operon promoter-proximal position than suggested on earlier maps and that traW is distal to traC. These results resolve a long-standing question concerning the relationship of traW to traC. The clones we have constructed are expected to be useful in elucidating the role of proteins TraC and TraW in F-pilus assembly.