Spliceosome

The spliceosome or spliceosome is a structure in the eukaryotic cell nucleus, which is involved in gene expression. It catalyzes the splicing, the intron ( non-coding portions ) are removed from the pre-mRNA and the exon ( encoding portions ) are combined. This produces the mRNA.

Structure

The spliceosome is comprised of 5 snRNP ( small nuclear ribonucleoprotein particles ), each of which comprises a snRNA ( small nuclear RNA), and a number of proteins. In addition, other non- snRNP factors - where there are proteins or protein complexes - involved in the construction. Overall, the mass of the assembled spliceosome is over 13 megadaltons.

Molding

The major distinction is spliceosome ( from the U1, U2, U4, U5 and U6 snRNP ) that is processed more than 95 % of human intron from minor spliceosome mainly processed, the so-called introns, ATAC, and in addition has a different composition snRNP ( U11 and U12 and U1 and U2 snRNP instead U4atac or U6atac instead U4 and U6 ) (see also splice ).

Process of splicing

The spliceosome is composed for each reaction together (ie, the removal of an intron ) from its individual parts directly on the primary transcript. It binds U1 snRNP in mammalian cells, the (small nuclear ribonucleoprotein U1) first the 5 ' splice site and initiates the further assembly of the spliceosome. The U2 snRNP binds with the help of other protein factors ( U2AF, U2 auxilliary factor) the branch point of the intron. Finally, the binding of the so-called tri - snRNP, a complex of the snRNP U4, U6 and U5 done. According to structural rearrangements in which other factors are involved, then generates active spliceosome, the snRNPs U1 and U4 are missing. snRNP U4 likely functions as an inhibitor, which is displaced by U6 snRNP. The catalytic center is formed from a helix of U2 and U6 snRNP. This catalyzes the first step (the first transesterification) of the splice, making the splicing intermediates arise ( free 5'- exon and 3' -exon Intronlariat ). After further changes in the structure and composition of the spliceosome finally done, the second reaction step, which leads finally to the release of the products and the disintegration of the spliceosome.