Structure of CRK10. A) Boxes represent untranslated and exonic regions, blue and green, respectively. A connecting line represents introns where the red section is the CaAp-containing intron 1. A red asterisk indicates the PTC introduced by intron 1 retention. Exon 2 encodes the transmembrane (TM) α-helix that separates Extra- from Intra-Cellular domains of the protein (as indicated). B) Intron 1 detail is shown. Uppercase green letters are exon sequence, as indicated, and red lowercase letters are intronic with predicted amino acid sequence shown below and culminating in the PTC (red asterisk). The CaAp region related to the 5aA2 aptamer is boxed. The core of the potential riboswitch sequence is underlined. C) The alternative transcript of CRK10 has a consensus for modification with a GPI-anchor at the ω position. The consensus includes (i) a string of prolines N-terminal to the ω residue is which are likely hydroxylated; (ii) required residues at the ω and ω+2 positions (red and blue respectively); (iii) a flexible moderately polar but uncharged region; and (iv) the final C-terminal string of non-polar residues heavy in aromatic amino acids [52, 53].