Figure 1. Structure and expression of recombinant cell-permeable reprograming factors.

(A–B) Group A reprogramming factors contain a 6× His tag (white), SV40 nuclear localization sequence (black) and MTD84 or MTD86 sequence (hatched) positioned (A). Numbered MTD sequences are positioned at the amino terminal end of human sequences—codon optimized for expression in E. coli (B). Solubility was scored on a 4 point scale ranging from highly soluble proteins with little tendency to precipitate (++++) to largely insoluble proteins (+). (C–D) Recombinant cell-permeable reprogramming factor proteins (group A: C; Group B: D) expressed in E. coli before (−) and after (+) induction with IPTG, and purification by Ni²⁺ affinity chromatography (P). Each group of the recombinant proteins (group A and group B) was run on the gels (C and D) under the same experimental conditions.