Процессинг РНК: различия между версиями

=== Полиаденилирование ===

Полиаденилирование заключается в присоединении к 3'-концу [[транскрипт]]а от 100 до 200 остатков адениловой кислоты, осуществляемом специальным [[фермент]]ом poly(A)-полимераза.

The pre-mRNA processing at the 3' end of the RNA molecule involves cleavage of its 3' end and then the addition of about 200 [[adenine]] residues to form a [[poly(A) tail]]. The cleavage and adenylation reactions occur if a [[polyadenylation|polyadenylation signal sequence]] (5'- AAUAAA-3') is located near the 3' end of the pre-mRNA molecule, which is followed by another sequence, which is usually '''(5'-CA-3')'''. The second signal is the site of cleavage. A '''GU-rich sequence''' is also usually present further downstream on the pre-mRNA molecule. After the synthesis of the sequence elements, two multisubunit [[protein]]s called [[cleavage and polyadenylation specificity factor]] (CPSF) and [[cleavage stimulation factor]] (CStF) are transferred from [[RNA Polymerase II]] to the RNA molecule. The two factors bind to the sequence elements. A protein complex forms that contains additional cleavage factors and the enzyme [[Polyadenylate Polymerase]] (PAP). This complex cleaves the RNA between the polyadenylation sequence and the GU-rich sequence at the cleavage site marked by the (5'-CA-3') sequences. Poly(A) polymerase then adds about 200 adenine units to the new 3' end of the RNA molecule using [[Adenosine triphosphate|ATP]] as a precursor. As the poly(A) tails is synthesised, it binds multiple copies of poly(A) binding protein, which protects the 3’end from ribonuclease digestion.<ref name=Hooper>{{Citation

|surname1 = Hames