Molecular model for messenger RNA splicing.

A molecular model is presented for a messenger RNA (mRNA) "splice region." The model requires cation coordination to reduce backbone-backbone electrostatic repulsion and it allows for every base residue on the pre-mRNA to be stacked in A-form helical geometry with a recognition element on the intron or exon (or both) sides of the splice junction. The two nucleotides involved in the initial steps of the cleavage-ligation mechanism must adopt a non-A-form geometry, which ideally positions reactive groups on the pre-mRNA for the necessary catalytic chemistry. The model is also consistent with available biochemical data on splicing reactions.