Ubiquitin, RNA transport into the nucleus is basic cell biology. There are numerous sources for this. I find it hard to believe that you couldn’t find reputable sources by typing in “mRNA tranfser into the nucleus” in the Google subject line.
I would paste links but I don’t think it is allowed here . Here are some sources:
PNAS published an article Nov 22 2005 titled “Mechanism of mRNA transport in the nucleus”
Pubmed published an article on Nov 2005 titled “Mechanism of mRNA transport into the nucleus”
An article published on viralzone titled “viral penetration in host nucleus” talking about viral RNAs, DNAs, etc pentratrating the nucleus.
An article titled “Extracellular mRNA transported to the nucleus” published on June 16 2021 on nature .com .