Dideoxynucleoside ddNTPs

DNA polymerases normally use 3 -deoxynucleotide triphosphates as substrates for polymerization. Given an adequate concentration of substrate, DNA polymerase synthesizes a long strand of new DNA complementary to the substrate. The use of this reaction for sequencing DNA depends on the inclusion of a single 2/3 -dideoxynucleoside triphosphate (ddNTP) in each of four polymerization reactions. The dideoxynucleotides ate incorporated normally in the chain in response to a complementary residue in the template. Because no 3 -OH is available for further extension, polymerization is... 

Nucleotides 2 -deoxynucleoside triphosphates (dNTPs) are purchased from Sigma (St. Louis, MO), and the 2, 3 -dideoxynucleoside triphosphates (ddNTPs) from Boehringer-Mannheim Biochemicals (Mannheim, Germany)... 

A number of nucleotide analog compounds function by blocking further chain growth at the replication fork. The 2 3 -dideoxynucleosides can be converted to the triphosphates (ddNTPs). In the case of bacteria, these are incorporated onto the 3 -hydroxyl end of a growing DNA chain, and because the new end now lacks a 3 hydroxyl, no further additions can occur. They are used in conjunction with DNA polymerase I in the dideoxy method of Sanger for determining DNA sequences. 

In molecular biology, TDT is used to effect the addition of complementary homopolymeric tails to vector and complementary DNA (cDNA) obtained from a mature mRNA template by reverse transcription and PCR amplification. An alternative application of TDT involves labehng of the 3 termini of DNA fragments with a P-labeled dNTP [36], a dideoxynucleoside triphosphate (ddNTP) [37], or a ribonucleoside triphosphate (rNTP) [38]. 

The key to the chain termination method is the addition of a 2, 3 -dideoxynucleoside triphosphate (ddNTP) to the synthesizing medium ... 

Dideoxynucleoside Triphosphate (ddNTP) Nucleotide lacking the 3 -hydroxyl function on its de-oxyribose sugar required for formation of bonds between nucleotides. 

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