Spliceosome

see also: Etymology of Spliceosome

ARN just like DNA is not free in the cores. Indeed, RNP (= Ribonucleic proteins) are large proteins related to the ARN pre-messenger enabling him to undergo the épissage, they are in some kinds the histones of the ARN. There are 20 proteins implied in these RNP. For example: to ARNsn ( small nuclear ) corresponds RNPsn. the splicéosomes , called pariculles of épissages, are made of RNPsn + ARN pre-messenger . At present, one does not know the exact interaction between ARN meadows-m and RNP Sn .

RNPsn have 3 functions:

alternate Épissage,
Structure of the splicéosomes and
Assembly of the splicéosomes

At human they are especially RNPsn U1 which intervenes in the splicéosomes.

The snRNP U2, U4, U5 and U6 have them also a great importance in the épissage of exons for the ARN messengers. U1 is used for the recognition of the sequence consensus GUAAGU contained at the beginning of the intron (after the exon of upstream). U2 is fixed then above, which requires energy and thus the hydrolysis of the ATP. Then come to set U4, U5 and U6 to form the complete splicéosome. U4 and U6 bound by hydrogen bond arrive together. U5, as for him, is fixed close to the site acceptor of épissage (thus before the exon of downstream), which allows the bringing together of both exons. thereafter, U6 will be disengaged of U4 to come to fix themselves on U2 and to form together the catalytic center of the splicéosome.

U3 catalyzes the maturation of ARNr 45s

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