Practice question

Once inside plant cytoplasm, the single-stranded T-strand is highly vulnerable to host nucleases that would destroy transgene before integration. VirE2 is an abundant single-strand DNA binding protein secreted independently via Type IV secretion system. It polymerizes cooperatively along entire T-strand length, forming protected filamentous T-complex with electron microscopically visible solenoidal structure. This coating masks phosphodiester backbone, prevents hairpin formation, and shields against DNases. Additionally, VirE2 interacts with host VIP1 and importin proteins to facilitate active nuclear import. VirB forms pilus, VirD1 assists nicking, so protection uniquely belongs to VirE2.