Domain structure and Phylogenetic distribution of the RT-fused Cas1 and its related proteins. (A) Schematic of the domain organization of HIV-1 RT, TeI4c group II intron RT, A. platensis type III-B RT-Cas1, MMB-1 type III-B RT-Cas1, and E. coli type I-E Cas1. Conserved RT motifs (1 to 7) are indicated in black boxes. Conserved motifs in mobile group II intron and non-LTR-retrotransposon RTs (0 and 2a) are labeled in red boxes. The YXDD sequence found in motif 5 represented with two aspartic acid residues is indicated by arrow. The X/Thumb domains commonly found in HIV-1 and group II intron RTs are indicated. Amino acid numbers are indicated below the bars. D, DNA binding domain. En, endonuclease domain. The image is taken from Silas et al. Science, 2016 (69). (B) Phylogenetic tree of Cas1 associated with RTs. The analysis is reconstructed with 148 Cas1 proteins. The identified clades with numbers are named and colored according to the RT-associated clade. The figure is taken and modified from Toro et al. Scientific Reports, 2017 (73).
