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. 2007 Aug 7;5(8):e209. doi: 10.1371/journal.pbio.0050209

Figure 5. Cross-Linking of Plastid mRNA 5′ UTR to Chloroplast and E. coli Ribosomes.

Figure 5

Radiolabeled psbA 5′ UTR was incubated with purified chloroplast or E. coli ribosomes, UV irradiated to cross-link mRNA, and then proteins were separated by SDS-PAGE. Protein size markers are indicated (in kDa). In E. coli, S1 is the main protein that is cross-linked to mRNA, while a small amount is cross-linked to another protein, presumably L1 (gray arrow on left lane). Chloroplast ribosomes have two proteins that clearly bind to mRNA, S1 and S2; two other bands are also labeled (gray arrows on right lane). One of these bands is L1, and the other appears as an incompletely denatured protein complex containing at least S5 and PSRP-7. Mass spectrometry was used to identify the protein component of labeled chloroplast ribosome bands (see Materials and Methods).