Molecular biology / antisense oligonucleotide design · BEGINNER LESSON
Gapmer
A gapmer is a chimeric antisense oligonucleotide, meaning a short synthetic single-stranded nucleic acid designed to bind a chosen RNA target. It has a central DNA-like gap that can recruit RNase H1, flanked by chemically modified wings that improve binding and stability.
What it is and what is measured
A gapmer is a designed antisense oligonucleotide, or ASO, used to reduce the amount of a specific target RNA. ASOs are short synthetic nucleic acid analogs that base-pair with complementary RNA through Watson-Crick base pairing, which is the normal pairing rules between bases. The important outcomes are how well the gapmer binds its target RNA, whether RNase H1 is recruited, and whether the target RNA is cleaved and lowered. The term ‘RNA cleavage’ means cutting the RNA strand so the cell can degrade it.
[1] Expanding the toolbox: Emerging antisense oligonucleotide ... [2] Survivin-Targeting Antisense Oligonucleotides in Cancer Therapy [3] Application of Antisense Oligonucleotides as an Alternative ... - PMC
How it works
The central DNA region of a gapmer forms a DNA-RNA duplex with the target messenger RNA (mRNA), and this duplex is recognized by endogenous RNase H1, a cellular enzyme that cuts the RNA strand. The flanking wings are usually chemically modified nucleotides, such as 2′-modified residues, that increase duplex stability and help the ASO stay attached long enough for cleavage to occur. This design keeps the RNase H1-recruiting ability of the DNA gap while adding nuclease resistance and stronger binding from the modified ends.
[1] Expanding the toolbox: Emerging antisense oligonucleotide ... [2] Survivin-Targeting Antisense Oligonucleotides in Cancer Therapy [3] Application of Antisense Oligonucleotides as an Alternative ... - PMC
Design features and limits
Gapmers are flexible because they do not have to bind one fixed motif such as a splice site, and they can be useful when complete knockdown of an RNA is desired. Their main limitation is off-target activity: partial matches can still recruit RNase H1 and cut unintended RNAs, so sequence choice and chemical modification must be designed carefully. More generally, ASO chemistry can shift behavior between cleavage and steric blocking, and some modifications improve stability but remove RNase H1 activity unless a DNA gap is kept in the middle.
[1] Expanding the toolbox: Emerging antisense oligonucleotide ... [2] Survivin-Targeting Antisense Oligonucleotides in Cancer Therapy [3] Application of Antisense Oligonucleotides as an Alternative ... - PMC
SEE THE IDEA
How a gapmer reduces target RNA
Chemically altered nucleotides improve stability and binding.
Central DNA-like region forms the RNase H1-recognized duplex.
Cell enzyme that cuts the RNA strand in the duplex.
Cut RNA is degraded, reducing the RNA available for protein production.
Modified wings support binding; the DNA gap recruits RNase H1; RNase H1 cuts RNA; the cell degrades the cut RNA.
A gapmer combines stable modified ends with a DNA core so the cell’s RNase H1 can recognize and cleave the paired RNA.
TRY IT YOURSELF
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.