Practice question

Eukaryotic pre-mRNAs contain conserved hexamer AAUAAA twenty to thirty nucleotides upstream of cleavage site, transcribed into RNA as polyadenylation signal essential for three prime end formation. Cleavage and polyadenylation specificity factor CPSF binds AAUAAA via WDR33 and CPSF30 zinc fingers recognizing sequence via base stacking interactions, while cleavage stimulation factor CstF binds downstream GU-rich downstream sequence element. Polyadenylation factors CFI, CFII, and endonuclease CPSF73 catalyze endonucleolytic cut. Signal AAUAAA is essential: single point mutation drastically reduces processing. Similar DNA sequence AATAAA in coding strand is classic Hogness box.