Seeing #mRNAs in cells, often involves the addition of MS2 binding sites in the 3' #UTR that can be detected with fluorescent #MS2 coat protein. The MS2 binding site repeats increase the size of the 3' UTR and can also affect the degradation of #RNA fragments containing them: https://pubmed.ncbi.nlm.nih.gov/30218101/

Longer 3' UTR induce the degradation of the RNA of interest through nonsense-mediated mRNA decay (NMD). This can be avoided by tethering #eRF3 or a mutant #PAB1.
https://www.biorxiv.org/content/10.1101/2022.02.05.479257v1.full