Do many SARS-CoV-2 chains (genomes/isolates) end in exactly 33 A's?Not really — very few, if any, do in practice. The poly(A) tail length is highly variable across isolates, samples, and even within the same infection (dynamic regulation during replication).
Studies using direct RNA nanopore sequencing (which captures native tails better) report median lengths around 47 nt for SARS-CoV-2 transcripts, with distributions often peaking ~30–60 nt.
In related coronaviruses (e.g., bovine CoV), tails vary from ~40–65 nt depending on infection stage (short early/late, peak ~65 nt mid-infection).
Most deposited SARS-CoV-2 sequences in databases like GISAID or GenBank either:Truncate the poly(A) tail entirely (common in consensus assemblies to avoid artifacts).
Include partial/short tails.
Or use the reference as a backbone and inherit the 33 A's artificially.
Exact 33 A's aren't a common natural occurrence; it's not like many independent isolates converge on precisely that number.