DCTP

Two new strands form as nucleotides that are complementary to those of the original strands are joined by phosphodiester linkages The sources of the new bases are dATP dGTP dCTP and dTTP already present in the cell... 

Add reverse transcriptase and substrates dATP, dTTP, dGTP, dCTP... 

After me ANPs (i.e., cidofovir, adefovir, and tenofovir) have been released (intra-or extraceUularly) from their prodrugs through the mtervention of infra- or extracellular esterases, they need only two phosphorylation steps to be converted to their active metabolites (i.e., HPMPCpp, PMEApp, and PMPApp), which will then compete with the natural substrates (dCTP for HPMPCpp, and dATP for PMEApp and PMPApp) for incorporation into me viral DNA (Fig. 6a). 

While metal-nitrogen and metal-oxygen bonded compounds dominate nucleobase coordination chemistry, examples in which metal-carbon bonds are formed have been identified. Early studies on the synthesis of metal-labeled DNA demonstrated that nucleotide-triphosphates, UTP, CTP, dUTP, and dCTP, can undergo mercury modification at C5 (82,83). The UTP derivative was also shown to act as a substrate for RNA polymerase in the presence of mercaptans (83). Later, guano-sine was shown to undergo mercury modification at C8 though, in this case, the purine was multiply substituted, 21 (84). 

Labeling of the RNA sample with a fluorescent nucleotide can be done either directly or indirecdy. In a direct labeling, one of the nucleotides (usually dUTP or dCTP) has a fluorescent moiety (either Cy3 or Cy5)... 

The pyrimidine nucleosides dUTP or dCTP can be modified at their C-5 position with a spacer arm containing a tag, such as a biotin group, and still remain good substrates for DNA polymerase. Enzymatic labeling with a biotin-modified pyrimidine nucleoside triphosphate is one of the most common methods of adding a detectable group to an existing DNA strand. 

Biotin-dUTP derivatives are formed by modification of the C-5 position of uridine. This location is not involved in hydrogen bonding activity with complementary DNA strands, thus hybridization efficiency is not immediately compromised. By contrast, biotin-dCTP or biotin-dATP derivatives involve modification of the bases at the N-4 position of cytosine and the N-6 position of adenine, locations directly involved in hydrogen bond formation with complementary bases. Thus, DNA biotinylation through the use of modified deoxynucleoside triphosphates to be incorporated into existing DNA strands may result in better activity of the probe if dUTP is used over dATP or dCTP. 

Figure 10.3. Mass array, (a) Primer binding (b) primer extension enzyme, ddATP and dCTP/ dGTP/dTTP addition (c) primer terminates (d) primer extension products ready for MALDI-MS (e) MS spectrum of primer extension products. Each addition of a nucleotide to the primer extension product increases the mass by 289 to 329 Da, depending on the nucleotide added. The mass difference is easily resolved by MALDI-TOF, which has the ability to detect differences as small as 3 Da. Printed by kind permission of Sequenom. (See color insert.)...

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