With regard to nucleic acids with repeating residues, could anyone provide a description of what the following sequences are, and the key differences between them:
- Poly(dA)
- Oligo(dA)
- Poly(A)
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$\begingroup$ Oligo means "few" in Greek, Poly means "many". If you look at the article on Oligonucleotide in Wikipedia, you will see that this is about as precise as you'll get. Another real world definition of oligo would be the size of synthetic DNAs that you can buy or have made at reasonable price, which judging from the article would seem to be at least 25 and not more than 200. I'd put an upper limit lower (e.g. 50), but it's quite subjective. $\endgroup$– DavidCommented Feb 4, 2019 at 17:48
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$\begingroup$ Although the Wikipedia article on polynucleotides says that according to the US NLM these latter start at 13. Hee hee. $\endgroup$– DavidCommented Feb 4, 2019 at 17:50
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1 Answer
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dN denotes deoxyribonucleoside (where N can be A, T, G or C). If there is no d prefix, then it denotes a ribonucleoside.
Regarding the difference between poly and oligo:
The former refers to having a large number of monomeric units whereas the latter means having a few monomeric units. There is no strict definition of the boundary between poly and oligo. Poly-A tails are typically about 70-80nt long in yeast (Eckmann et al. 2010). So it logically follows that anything shorter than that should be called an oligo-A. Chemically synthesized stretches of DNA are often referred to as oligos even though nowadays one can synthesize more than 80nt long DNA/RNA. Moreover, a stretch of As in some mammalian mRNAs smaller than the usual length of ~150-250 is still referred to as a short poly-A tail instead of an oligo-A tail (Jalkanen et al. 2014; there are many more examples).
Additionally, even if the cutoff is, let's say, 100 units, it doesn't apply to proteins. A protein with 100 amino acids is still considered a polypeptide and not an oligopeptide. For peptides, the cutoff is generally around ~30.
So, I would conclude that the usage of these prefixes is quite contextual.