Figure 15-9b: Evolutionary reconstruction of the deleted coat-protein initiator-hairpin in MS2 RNA. (A) At the sequence level and (B) at the level of secondary structure. In the starting deletion mutant (bottom left) 19 nts have been deleted and coat-protein synthesis could no longer be detected. In Rev 2.1 a specific 14 nt duplication (bold italics) has occurred that restores both the initiator-hairpin and the A-protein terminator-hairpin as well as the SD sequence. Panel B shows that in Rev 3.1 and Rev 2.2 the terminator is further polished by replacing the G•G mismatch by G•U and G-C, respectively (black boxes). Rev 2.3 acquires another 4 nts that enlarges the distance between the two hairpins. In Rev 2.4, finally, the SD sequence is extended with one nt and the distance between the hairpins is back to wild type but for one nt. In Rev 1.1 the SD sequence and the initiator hairpin are restored by a 6 nt deletion. The terminator hairpin is sacrified. In Rev 1.2. The same A → G substitution is selected as in Rev 2.4 and Rev 3.1. This change extends the SD sequence by one nt, but it is not sure if we understand this. In panel A stop codon of the A-protein gene and start codon of the coat protein are shaded. SD sequence is in bold and suppressor mutations are in lower case. In panel B suppressor mutations are in black boxes, insertions are in bold italics and SD and coat-start codon are boxed. Note that the starting mutant has two accidental base substitutions three and six nts 3' to the start codon. (for better image quality, click here for tif image, which may be quite large; may also require screen refreshing plus special software to view; or view larger tif in separate window)

Figure 15-1, Figure 15-2 ( ab ), Figure 15-3, Figure 15-4, Figure 15-5, Figure 15-6, Figure 15-7, Figure 15-8, Figure 15-9 ( ab ), Figure 15-10, Figure 15-11, Figure 15-12, Figure 15-13,

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