This is true, but perhaps worth noting the nuclear transport function of polyA tails don't come into play for coronavirus. The payload of coronavirus is a positive-sense single-stranded RNA. Which means it does not need to enter the nucleus for preprocessing and can basically just start replicating shortly after entering a cell. See diagram...
There might be a software analog to another polyA tail feature: the provision of a 'shelf-life'. Each replication cycle removes a few adenosines, and at a certain point the tail sequence is too short to recruit protection and the RNA is ushered into the degradation pathway.
I don't think the genome has a specific length of the tail (33 is a consensus length)
During genomic assays, the poly a tail will not be a specific length, but a single consensus sequence is still provided.
This was also posted in the first comment:
> Similar to eukaryotic mRNA, the positive-strand coronavirus genome of ~30 kilobases is 5’-capped and 3’-polyadenylated. It has been demonstrated that the length of the coronaviral poly(A) tail is not static but regulated during infection; however, little is known regarding the factors involved in coronaviral polyadenylation and its regulation. Here, we show that during infection, the level of coronavirus poly(A) tail lengthening depends on the initial length upon infection and that the minimum length to initiate lengthening may lie between 5 and 9 nucleotides. By mutagenesis analysis, it was found that (i) the hexamer AGUAAA and poly(A) tail are two important elements responsible for synthesis of the coronavirus poly(A) tail and may function in concert to accomplish polyadenylation and (ii) the function of the hexamer AGUAAA in coronaviral polyadenylation is position dependent. Based on these findings, we propose a process for how the coronaviral poly(A) tail is synthesized and undergoes variation. Our results provide the first genetic evidence to gain insight into coronaviral polyadenylation.
Peng Y-H, Lin C-H, Lin C-N, Lo C-Y, Tsai T-L, Wu H-Y (2016) Characterization of the Role of Hexamer AGUAAA and Poly(A) Tail in Coronavirus Polyadenylation. PLoS ONE 11(10): e0165077
The polyA tail isn't even coded by the genome, it's added after transcription by a processive polyadenylation multiprotein complex with the final tally being the result of partially stochastic processes. So yeah, agreed, the number of adenines is variable.
