Figure 2From: Unification of Cas protein families and a simple scenario for the origin and evolution of CRISPR-Cas systemsThe RRM fold of RAMPs and Cas2. The RRM fold domains of Cas2 and the three major RAMP groups proposed in the text are shown in cartoon representation with their N- and C- termini indicated. In Cas7, the insertions into the core of the RRM fold are shown in a darker shade. In the RAMPs with two RRM fold domains, these are respectively labeled as N(-terminal) and C(-terminal). The distinct C-terminal domains of Cas5 and Cas6f (Csy4) are also shown. In Cas6f, the glycine-rich loop, which is embedded in a beta-hairpin in contrast to the typical helix-strand element, is colored orange. Note the "horizontal" packing of the first helix of the core RRM fold against the 4 strand sheet, which is one of the characteristic structural features of the RAMPs (apparent in Cas7, Cas6, Cas6e and Cas5). The following PDB ids were used to generate these representations: 2I0X (Cas2);_3PS0 (Cas7); 3I4H (Cas6); 1WJ9 (Cas6e/CasE); 3KG4(Cas5); 2XLJ (Cas6f/Csy4).Back to article page