Trans- splicing mechanism

Mechanism of Trans-Splicing the Spliced-Leader RNAs... 

Mechanism of Trans-Splicing Required snRNP Cofactors... 

Figure 4 Mechanism of trans-protein splicing, (a) Initial association of the intein halves to form a functional intein. (b) Activation of the N-terminal splice-junction via an N-S acyl shift, (c) Formation of a branched intermediate upon transthioesterification. (d) Branch resolution and intein release by succinimide formation. Spontaneous S-N acyl rearrangement yields the processed product with a native peptide backbone.

Since the 9-kb and 4-kb HIV mRNAs contain splice sites, they can be viewed as Incompletely spliced mRNAs. However, as discussed earlier, association of such Incompletely spliced mRNAs with snRNPs In spllceosomes normally blocks their export from the nucleus. Thus HIV, as well as other retroviruses, must have some mechanism for overcoming this block, permitting export of the longer viral mRNAs. Some retroviruses have evolved a sequence called the constitutive trans port element (CTE) that binds to the mRNA-exporter with... 

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