Overview Only in eukaryotes pre-processed transcript = hnRNA Process capping 5' end 7-methylguanosine cap occurs before transcription has finished functions to help in ribosomal binding also protects against degradation 3' end polyadenylated (poly-A) tail added by poly-A-polymerase functions to protect from degradation some viruses can steal host cell caps so that the viral mRNA gets translated splicing process of intron removal mediated by the spliceosome composed of small nuclear ribonucleoproteins (snRNPs) lariat is formed adjacent exons are attached alternative splicing one hnRNA can be spliced differently to produce different protein products this requires conserved sequences including GU at the beginning of the intron AG at the end of the intron mutations that create new splice sites (AG) in the middle of the intron can lead to abberant splicing that creates new nonfunctional proteins longer proteins than the wildtype variant Location occurs in nucleus after transcription only processed RNA is transported out of the nucleus