There's clear evidence of epigenetics playing a role in brain activity, though these are more linked to hormonal responses such as stress. It's also been proven that RNA transcripts are used to trigger maternal instincts when a zygote is present in a mother: https://en.wikipedia.org/wiki/Epigenetics

Scientists have already modeled memory retrieval using current neural network models. There's literally videos on youtube demonstrating this. I'd be surprised if RNA was used to encode memories to the extent OP is suggesting: there would have to be a mechanism for storing this RNA inside cells or there would be evidence of random strands of RNA floating around in the body. We would have been found it a long time ago, and scientists would also be able to decode it if these strands of RNA were standardized and could be transferred person to person.

Though the way evolution works and how complicated the body is, it could be occurring in a small sub process in a neurons somewhere in the body. though this would likely be tied to hormonal responses or something equally boring.