RNA structure diagrams of L2449 group I introns in Physarales clades. Paired elements (P1 to P9) are indicated according to the consensus of L2449 group I introns in myxomycetes . The intron core and exon sequences are shown in upper case and lower case letters, respectively. Arrows indicate the 5’ splice site (SS) and the 3’ SS. Sizes of extension sequences at peripheral P-regions are indicated. The synapomorphy at the intron G-binding site in P7 is boxed. A. Clade I (P. pusillum CJA3, B. melanospora Pr-1) L2449 introns that contain the G-binding site motif UCG-CA (green box). B. Clade II (P. polycephalum Wis1, B. utricularis) L2449 introns that contain the G-binding site motif ACG-CU (yellow box). C. Clade III (P. compressum CJ1-1, P. didermoides) L2449 introns that contain the G-binding site motif AUG-CU (blue box). D. Schematic organization of large extension sequences in P2 and P9 of the 2483 nt L2449 intron in P. didermoides (Clade III). The 503 nt P2 extension contains five copies of an approximately 60-nt A motif. The 1268 nt P9 extension has a more complex organization of three different motifs of approximately 40 nt (B motif, 3 copies), 100 nt (C motif, 5 copies) and 55 nt (D motif, 2 copies), respectively. Here, motif C is composed by three sub-motifs (a-b-a-c), and related to motif D (a-c).