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. 2021 Jul 14;13(7):487. doi: 10.3390/toxins13070487

Figure 1.

Figure 1

Schematic illustration of a CAG-repeat expansion during DNA replication, its transcription into RNA and three-dimensional RNA folding dependent on the CAG-repeat length. Upper part of the picture: During DNA replication, the polymerase uses the template strand (blue) to synthesize a nascent strand (red). CAG-repeat expansion during replication can be explained by strand-slippage. The polymerase detaches from the template strand and reattaches such that a part of the repeat sequence is looped out. Due to this misalignment, the nascent strand has an increased number of CAG repeats. Lower panel: the CAG repeat containing mRNA folds into a three-dimensional structure that depends on the repeat length. mRNA with either normal (left) or mutant (right) CAG repeat numbers are shown. The mutant CAG repeat folds into a characteristic hairpin structure that sticks out to the side. The mutant CAG-repeat hairpin is highlighted in red and the corresponding short CAG-repeat sequence in the normal transcript is highlighted in green. Created with BioRender.com and the RNA Folding Form V2.3 (http://www.unafold.org/mfold/applications/rna-folding-form-v2.php, accessed on 22 March 2021).