http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2517594/
C3 spacer (3 hydrocarbons) CPG is a standard primer modification available from most suppliers of custom oligonucleotides. Adding this modification to the 3'-end of an oligonucleotide prevents elongation during a PCR without noticeably influencing its annealing properties. Because oligos are synthesized from a 3' to 5' direction, all molecules will be modified with the 3' modification. Modifying the 3'- end with a phosphate group (as chosen by Liles et al. [35]), a phosphate ester, or using an inverted 3'-3' linkage would also prevent elongation. However, side reactions during deprotection of the oligonucleotide or enzymatic impurities may free the 3'-hydroxyl group to a small extent, and these methods are not so effective in blocking as C3 spacers CPG [38,39]. |
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