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Home >> Biotechnology and Genomics >> DNA-Based Molecular Markers in Biotechnology >> Taqman Assay

Taqman assay.
In this assay, an oligonucleotide probe is labelled with a fluorescent reporter molecule (e.g. FAM or TET) at 5' end and a quencher (e.g. TAMRA) at the 3' end.

The TaqMan probe after hybridization to the template DNA is degraded at its 5' end during extension phase of PCR due to exonuclease activity of Taq polymerase enzyme (TaqMan polymerase), so that the reporter is released leading to a rise in fluorescence signal. However, when due to the presence of an SNP, the probe mismatches with the template leading to a failure in duplex formation, no such degradation at 5' end of the probe is possible and there is no rise in fluorescence signal. Different combinations of reporters and quenchers, will also permit multiplexing so that as many as six SNPs can be scored in a single PCR reaction.

The risk of given the need to administer treatment frequently (because of the inability of immune response to these vectors is negligible. This is an important consideration adenovirus to integrate into chromosomal DNA). They also have advantage that they can accept much larger inserts(up to 35kb).
It is clear that for a wide variety of cell types, adenovirus (Ad) gives more efficient gene transfer compared with other systems, especially in vivo. Ad vectors can transfer genes to both proliferating and quiescent cells. Following delivery, transgene expression is at a high level, but is transient , being low or undetectable in most tissues after two weeks.

This is because Ad vectors do not integrate and for safety reasons are disabled for replication. The expression profile with first generation. Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing, for most immunotherapy strategies and for some acute diseases. The first generation vectors have an insert –size limit of ~7.5kb.

The expression profile with first generation. Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing, for most immunotherapy strategies and for some acute diseases. The first generation vectors have an insert –size limit of ~7.5kb. The promoter used most frequently with Ad (and indeed all other vectors) is derived from cytomegalovirus(CMV), which gives strong expression in many cell types.

Ad gives particularly, efficient gene transfer to the liver, such that dissemination form the site of local injection(such as tumours) and consequent liver transfection is the most serious safety concern. The most serious limitation of Ad vectors stems from their tendency to elicit strong immune and (at high doses) inflammatory responses. Single, large doses of Ad provoke neutralizing antibody response directed to proteins of the viral particle, which prevent binding to target cells and abrogate gene transfer upon repeat dosing by systemic administration routes in animals.

Overall, Ad is the easiest viral vector from the manufacturing viewpoint, allowing the production of large quantities with titre and in relatively robust formulations. Nevertheless, Ad shares with other viral vectors the problem that first-generation vector preparations are contaminated with replication competent virus (RCV), which arises through recombination between viral sequences in the vector and in the chromosome of the producer cells. Many of the clinical studies giving encouraging signs of efficacy use Ad vectors.
The expression profile with first generation.

Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing, for most immunotherapy strategies and for some acute diseases. The first generation vectors have an insert –size limit of ~7.5kb. The expression profile with first generation. Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing

The most advanced of these delivers the wild-type gene for the tumour suppressor P53 for induction of tumour –cell killing. A series of phase II studies is underway, testing this recombinant virus alone and in combination with chemotherapies for the local management of various cancers.The expression profile with first generation. Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing, for most immunotherapy strategies and for some acute diseases.

The first generation vectors have an insert –size limit of ~7.5kb.The expression profile with first generation. Ad vectors is not suitable for the long-term correction of chronic diseases but is adequate for direct cell killing, for most immunotherapy strategies and for some acute diseases. The first generation vectors have an insert –size limit of ~7.5kb.

 

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