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What is a carrier molecule?

A carrier molecule is typically involved in the transport of other biological compounds such as proteins, DNA or RNA, electrons, or protons including ions. For example, carrier proteins can transport other molecules such as ions, sugar, fat, or peptides through the cell membrane.

For the isolation of
DNA and RNA using mini purification kits, the use of carrier DNA is recommended when expected yields are low, for example, below ten (10) ng.

DNA carrier molecules such as poly-dA (
poly-(A)), poly-dT (poly-(T)) or poly-dA:dT (poly-(AT)) should be used for RT-PCR. Other carriers such as herring sperm DNA may interfere with PCR by possibly nonspecific binding of primers.

Poly-(A) may interfere with oligo-dT primers. In this case, use a different carrier. 

Poly-(A) refers to the poly-(A) tail at the 3'-end of oligonucleotides consisting of a repetitive sequence of adenine nucleotides. The 3'-end of nearly all eukaryotic mRNAs include a string of 50 to 250 adenylate residues, called poly-A tail.

Typical concentrations of carriers are >10 μg/ml. The size distribution of the carrier molecules ranges from 100 base pairs ten (10) kilobases (kb). But optimal amounts used need to be experimentally determined for each application.

Beránek et al., in 2016, investigated the effect of carrier molecules on the extraction yields of circulating tumor DNA (ctDNA) from plasma samples. Their results revealed that poly-(A) worked best and therefore is the carrier molecule of choice when extracting low levels of DNA or RNA from biological samples.

Alternatively, a linear polyacrylamide (LPA) is also an option for DNA and RNA template coprecipitation. Gaillard and Stauss precipitated DNA with ethanol in the presence of LPA to improve yields. Sachdeva and Simm demonstrated the precipitation effect of LPA during their isolation and characterization of X-DING-CD4 cDNA using touch-down PCR.


Carrier molecules used for immunization are:

  • Protein carries: KLH, BSA, Thyroglobulin, OVA, Tetanus and Diptheria Toxoids
  • Liposome-oligonucleotide conjugates
  • Synthetic or natural polymers (dextran, agarose, poly-L-lysine), or
  • Synthetically designed organic molecules (dendrimers).
The primary criterion for a carrier molecule used for immunization is the potential for immunogenicity. A suitable functional group for conjugation with oligonucleotides, DNA, RNA, nucleic acids, proteins, or peptides should be available for conjugation as well.

Reference

Beránek M, Sirák I, Vošmik M, Petera J, Drastíková M, Palička V. Carrier molecules and extraction of circulating tumor DNA for next generation sequencing in colorectal cancer. Acta Medica (Hradec Kralove). 2016;59(2):54-58. doi:10.14712/18059694.2016.54. [Pubmed]

Claire Gaillard, François Strauss, Ethanol precipitation of DNA with linear polyacrylamide as carrier, Nucleic Acids Research, Volume 18, Issue 2, 25 January 1990, Page 378.[Link]

Poly-(A); Poly-A

Sachdeva R, Simm M. Application of linear polyacrylamide coprecipitation of denatured templates for PCR amplification of ultra-rapidly reannealing DNA. Biotechniques. 2011 Apr;50(4):217-9. [PMC]

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