Figure 4.

Elements regulating the splicing of pre-messenger RNA (mRNA). Major regulatory elements of pre-mRNA splicing, namely donor/acceptor splice sites and polypyrimidine tract, are shown with the corresponding trans-acting factors (U1, U2 snRNPs and U2AF₆₅-₃₅). The Exonic Splicing Enhancer (ESE), Silencer (ESS), Intron Splicing Enhancer (ISE) or Intron Splicing Silencer (ISS) sequence(s) positively or negatively contribute to exon recognition through interaction with serine–arginine-rich (SR) proteins and heterogeneous ribonuclear particles (hnRNPs), respectively.