Rearrange

FINAL PROTEIN FORMED FIGURE 12.18 Branched Intermediate during Intein Splicing

The intervening intein segment splices itself out in two stages. The intein has a Cys or Ser at the boundary with extein 1 and a basic amino acid at its boundary with extein 2. The downstream extein (#2) has a Cys residue at the splice junction. Extein 1 is cut loose and attached to the sulfur side chain of the cysteine at the splice junction. This forms a temporary branched intermediate. Next the intein is cut off and discarded and the two exteins are joined to form the final protein.

FIGURE 12.19 Intein Splicing Reconstitutes the DnaE Protein

The DNA coding for the DnaE protein of Synechocystis is transcribed and translated into two separate proteins, each containing an intein and an extein. The exteins of the two proteins are spliced together by the inteins. During splicing both inteins are lost.

Chromosome with split dnaE gene

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