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Fig. 2 | Biology Direct

Fig. 2

From: Domestication of self-splicing introns during eukaryogenesis: the rise of the complex spliceosomal machinery

Fig. 2

Evolution of the Sm and Lsm rings. a Tree depicting the scenario on the evolution of the spliceosomal Lsm and Sm proteins, as proposed in [90]. b Possible scenario for the evolution of the Lsm and Sm rings. A homoheptameric Lsm ring interacted with the trans-acting U6 snRNA, thereby facilitating splicing of degenerating self-splicing introns. While the Lsm ring became heteromeric upon duplication and subfunctionalisation of the Lsm protein, the trans-acting U2 and U5, which all originated from the introns, and U1 and U4 snRNAs formed RNP complexes with the Lsm ring. Upon duplication of the ring, U6 snRNA was bound by the Lsm ring, whereas the other snRNAs formed a complex with the newly formed Sm ring, followed by the addition of other proteins

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