Characterization of the NSE6 subunit of thePhyscomitrium patensPpSMC5/6 complex

Structural Maintenance of Chromosome (SMC) complexes are molecular machines ensuring chromatin organization at higher levels. They play direct roles in cohesion, condensation, replication, transcription and DNA repair. Their cores are composed of long-armed SMC, kleisin, and kleisin-associated KITE or HAWK subunits. Additional factors, like NSE6 within SMC5/6, bind to SMC core complexes and regulate their activities. To characterize the NSE6 subunit of moss Physcomitrium patens , we analyzed its protein-protein interactions and Ppnse6 mutant phenotypes. We identified a previously unrecognized sequence motif conserved from yeast to humans within the NSE6 CANIN domain that is required for interaction with its NSE5 partner. In addition, the CANIN domain and its preceding sequences bind and link SMC5 and SMC6 arms, suggesting its role in SMC5/6 dynamics. Both Ppnse6dCas9_3 and Ppnse6KO1_47 mutant lines exhibited reduced growth and developmental aberrations. These mutants were also sensitive to DNA-damaging drug bleomycin and lost a significant portion of rDNA copies, suggesting conserved architecture and functions of SMC5/6 complexes across species.