Fig. 8: Model of the formation of the Hermes transpososome in cells.

a Schematic of the organization of the core of the two-left-end (LE-LE) and two-right-end (RE-RE) Hermes transpososomes observed by cryo-EM. In the LE-LE transpososome, the LE-TIR interacts with the catalytic center of one Hermes protomer, the LE-STR1-STR2 palindrome and the LE-STR3 interact with three BED domains from three Hermes protomers belonging to three dimers, and the LE-DNA 3’-end interacts with the opposite Hermes dimer. The LE-DNAs interact with the transposase assembly in an antiparallel orientation. In the RE-RE transpososome, the RE-TIR interacts with the catalytic center of one Hermes protomer, and the RE-DNA 3’-end interacts with the opposite Hermes dimer. The RE-DNA does not interact with BED domains. The RE-DNAs interact with the transposase assembly in parallel orientation, with both RE-TIRs present in the same Hermes dimer. b Proposed model of the formation of the Hermes transpososome in cells. The LE is first recognized by the transposase assembly, because of its higher affinity conferred by its quasi-palindromic STR1-STR2 motif (one-end complex). Once the LE is bound, the RE is only a few kilobase away at the other end of the transposon and can then be recognized solely based on the sequence of its TIR. The unspecific interaction of the 3’-end of both LE and RE might support the formation of the transpososome. Host factor DNA-bending proteins may interact with the transposon to facilitate end pairing. When both TIRs are synapsed inside the same Hermes dimer (paired-end complex), the transpososome is in the proper configuration to perform its cut-and-paste transposition chemistry.