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. 2024 Jul 16;21(9):1634–1645. doi: 10.1038/s41592-024-02335-1

Fig. 4. Cryo-EM of RORC 3ʹ mRNA is consistent with dynamic exchange in a shallow energy landscape.

Fig. 4

a, Cryo-EM of wild-type RORC mRNA, 77-GA mutant and 117-AC mutant, as representative examples of qualitatively different compact and extended RNA-like particles. Different morphologies are indicated by numbered labels. Source micrographs were phase-flipped, Gaussian filtered and contrast inverted for display (see Extended Data Fig. 5). Scale bars, 50 nm. b, Three structural classes of the refolded RORC 3ʹ mRNA element as determined on cryo-EM processing, with RNA-like features (top). Further cryo-EM imaging and 3D classification of the 77-GA mutant (middle) and 117-AC mutant (bottom) indicate that Class A is present in wild-type and 77-GA samples but absent from the 117-AC sample, and Class B is conversely present in wild-type and 117-AC samples but absent from the 77-GA mutant. Class C is common to all three samples. We thus assign Class A as the conformation 1 state, and Class B as the conformation 2 state. We propose Class 3 to represent a partly folded intermediate that is not disrupted in the mutated constructs.