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. Author manuscript; available in PMC: 2013 Jul 1.
Published in final edited form as: Br J Haematol. 2012 May 18;158(2):165–173. doi: 10.1111/j.1365-2141.2012.09158.x

Figure 1. Normal and aberrant pre-mRNA splicing.

Figure 1

A. Pre-mRNA splicing is a two step process catalyzed by spliceosomes and specified by three RNA sequence elements called the 5’ splice site, the 3’ splice site and the branch site. In the first step of the reaction, the 2’ hydroxyl group of the adenosine residue at the branch site attacks the 5’ splice site to form a bi-partite intermediate consisting of the upstream exon and a lariat molecule containing the downstream exon joined to the intron. In the second step, the upstream exon attacks the 3’ splice to yield the ligated exons and the excised intron in lariat form.

B. The splicing pattern of genes can vary due to normal alternative splicing choices or due to mutations of the cis-acting RNA sequence elements or the trans-acting splicing factors. The various outcomes of alternative or pathological splicing events are diagramed. In most cases, misplicing will lead to degradation of the aberrant mRNA either in the nucleus or through nonsense mediated decay in the cytoplasm.