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Influence of stereochemistry of the 3′-terminal phosphorothioate (PS)-modified primers was studied in a single base extension (SBE) assay to evaluate any improvements in specificity. SBE reactions were catalyzed by members of the high fidelity Pfu family of DNA polymerases with (exo+) or without (exo−) 3′ → 5′ exonucleolytic activity. The diastereomerically pure PS-labeled primers used in these studies were obtained either by the stereospecific chemical synthesis invented in our laboratory or by the more conventional ion-exchange chromatographic method for separation of a mixture of diastereomers (RP and SP). When the SBE reaction was performed in the presence of mispaired 2′-deoxyribonucleoside triphosphates (dNTPs), the “racemic” 3′-phosphorothioate primer mixture resulted in a lower level of 3′ → 5′ exonuclease-mediated cleavage products in comparison to the SBE reactions carried out with the corresponding unmodified primer. When the diastereomerically pure RP 3′-phosphorothioate primer was examined, the results were largely the same as for the racemic 3′-phosphorothioate primer mixture. In contrast, a 3′-PS primer of SP configuration displayed significantly improved performance in the SBE reaction. This included the lack of 3′ → 5′ proofreading products, less mispriming, and improved yield of incorporation of the correct nucleotide. [ABSTRACT FROM AUTHOR]

Human cytomegalovirus (HCMV) is a widespread agent causing a life-long persistent and generally asymptomatic infection in immunocompetent individuals. In contrast, immunocompromised subjects are the most susceptible group to experience HCMV disease. First genes to be expressed during the replication cycle are the immediate early (IE) genes, the products of which have pleiotropic effects on host cell metabolism. Aim of this study was to compare two set of primers in the optimization and standardization of a RT-PCR assay for qualitative detection of mRNA encoded by the IE gene UL123 (IE1). The RT-PCR assays were then used to evaluate the UL123 gene expression in 29 peripheral blood leukocyte (PBL) samples obtained from 14 renal transplant recipients. In particular, 21/29 (72.4%) were positive with set A of primers vs. 24/29 (82.8%) with set B. Only one sample were negative with set B and positive with set A. Twenty-four of 29 samples (82.8%) were pp65-antigaenemia positive: 21 mRNA-UL123 positive with set A vs. 22 with set B; all viraemia-positive patients were mRNA-UL123 positive with both set A and B. Five of 29 samples were pp65-antigaenemia negative: 1 mRNA-UL 123 positive with set A vs. 2 with set B; all of them were viraemia-negative. These two RT-PCR assays could provide a reliable, rapid and sensitive system enabling the detection and identification of UL123 transcripts and could be usefully employed to study the pathogenesis of HCMV-related diseases. [ABSTRACT FROM AUTHOR]

Site-directed mutagenesis (SDM) is a powerful tool for exploring protein structure and function, and several procedures adjusted to specific purposes are still being developed. Herein we describe a straightforward and efficient method with versatile applications for introducing site-specific alterations in any deoxyribonucleic acid (DNA) sequence cloned in a plasmidic expression vector. In this polymerase chain reaction (PCR)-based SDM method, forward and reverse primers are used to amplify the plasmid containing the sequence of interest. The primers are designed so that the desired modifications are introduced at the 5′ end of one of the primers, whereas the other primer starts with the nucleotide at position (−1) of the one to be modified. The PCR is carried out using Pfu DNA polymerase. The blunt-ended PCR-generated DNA fragment is self-ligated and used to transform Escherichia coli. Mutant clones are screened by colony hybridization using the mutagenic primer as probe and the presence of the mutation is confirmed by direct DNA sequencing. This procedure was used efficiently to introduce substitutions, deletions, and insertions in the DNA sequences coding for a recombinant form (scFv) of antibody 107 specific of the human CR3 molecule, the rat α integrin CD11b A-domain and the human CD8β cloned in pPICZαB, pGEX-2T, and CDM8 expression vectors, respectively. [ABSTRACT FROM AUTHOR]

Amplification of DNA or RNA sequences using the polymerase chain reaction (PCR) or reverse transcriptase PCR (RT-PCR) requires primers of an appropriate length to be designed. Two hexamer restriction primers, denoted as E101 and H301, which correspond to sequences of EcoRI and HindIII recognition sites, respectively, were selected and used as primers in PCR and RT-PCR. We first applied the restriction primers to the plasmid DNA and bacterial ( Pseudomonas) and plant ( Cymbidium) genomic DNAs. We observed positive DNA amplifications with the recombinant plasmid DNA and bacterial and plant genomic DNAs. Purified viral RNA was used for template in the RT-PCR with the primers and successful DNA amplification was obtained. These results suggest that the 6-mer restriction primers can be useful for new applications in PCR. [ABSTRACT FROM AUTHOR]