Fig. 1: IS621 synaptic complex structure.

a, Schematic of the IS621 insertion sequence element. LD, left donor; RD, right donor; LE, left end; RE, right end, LT, left target; RT, right target; SL, stem loop. b, Domain structure of the IS621 recombinase. CC, coiled-coil domain. c, Schematics of bRNA-guided dDNA and tDNA recognition. The 5′ stem loop and the linker region in the bRNA are omitted, as the TBL and DBL in a single synaptic complex are derived from two different bRNA molecules. BS, bottom strand; TS, top strand. d, Nucleotide sequences of the bRNA-complementary regions in the tDNA and dDNA. Mismatched (MM) nucleotides introduced to the top strands for the structural analysis are shown as lowercase letters. Bottom strands are indicated by asterisks. e,f, Structures of the IS621–bRNA–dDNA–tDNA synaptic complex (e) and the bRNA–dDNA–tDNA complex (f). Disordered regions are indicated by dotted lines, and the CT core dinucleotides (positions 8 and 9) are numbered. In f, the S241 residues are shown as stick models. g,h, Structures of the tetramer (g) and monomer (h) of the IS621 recombinase. The catalytic residues are shown as space-filling (g) and stick (h) models. In h, the core α-helices and β-strands in each domain are numbered. In d,f, DNA cleavage sites are indicated by yellow triangles. In e,g, the active sites with the ordered and disordered S241 residues are indicated by red solid and dashed circles, respectively.