Figure 4.

Electron spectroscopic images of SR protein/cTnT pre-mRNA incubation reactions show that SR proteins are able to create a loop in the RNA between the two functional exons. SR proteins and UP5/WT6 RNA were incubated under similar conditions as in Fig. 4, and fractions of these reactions were placed directly on EM grids and analyzed with a Zeiss EM 902 transmission electron microscope. The images were recorded at 120 eV. Linear molecules are shown in a, and structures compacted because of RNA secondary structure are shown in b. Loop structures involving the RNA with two functional exons are shown in c–f, one loop involving the RNA with the mutation in exon 5 is shown in g, and RNA with a mutation in exon 6 is shown in h. (Bar = 55 nm.)