Spacer 9 is a triethylene glycol chain that is 9 atoms long (6 carbons + 3 oxygens), and is used to incorporate a spacer arm into an oligonucleotide. Spacer 9 can be incorporated in consecutive additions whenever a longer spacer is required. Spacer 9 has been used to form non-nucleotide bridges in hairpin loops in oligonucleotides (1), for linking oligonucleotides to epitopes for drug development (2), and for solid-phase immobilization of hybridization probes (3). Multiple incorporation of Spacer 9 has been used to form long, flexible linker arms between the two domains (double-helix forming and triple-helix forming, respectively) of a bifunctional DNA oligonucleotide, in order to maximize the binding flexibility of the two domains for their respective targets (4). This oligo was used to form a peptide nucleic acid (PNA)-DNA conjugate for use in site-directed recombination applications.
1. Nelson, J.S., Giver, L., Ellington, A.D., Letsinger, R.L. Incorporation of Non-Nucleotide Bridge into Hairpin Oligonucleotides Capable of High-Affinity Binding to the Rev Protein of HIV-1. Biochemistry. (1996), 35: 5339-5344.
2. Palma, E., Klapper, D.G., Cho, M.J. Antibodies as Drug Carriers III: Design of Oligonucleotides with Enhanced Binding Affinity for Immunoglobulin G. Pharm. Res. (2005), 22: 122-127.
3. Beattie, W.G., Meng, L., Turner, S.L., Varma, R.S., Dao, D.D., Beattie, K.L. Hybridization of DNA targets to glass-tethered oligonucleotide probes. Mol. Biotechnol. (1995), 4: 213-225.
4. Rogers, F.A., Vasquez, K.M., Egholm, M., Glazer, P.M. Site-directed recombination via bifunctional PNA-DNA conjugates. Proc. Natl. Acad. Sci. USA (2002), 99: 16695-16700.