3' dA Blocked 40 nmol scale, 1 modification

Exonuclease activity, mainly at the 3’-terminus, is the primary cause of oligonucleotide degradation. The introduction at the 3’ terminus of 3’- deoxynucleosides bases, 2’, 3’-ddC or 3’ 3’-inverted base enhance resistance to degradation. These modifications also block the 3’-terminus from extension during polymerase extension (eg. PCR amplification) and allow cloning of specific alleles using 3’-blocked and 3’-OH oligonucleotides mixture for polymerase amplification of specific alleles.