Virus-like complexes of supercoiled plasmid DNA with diblock polypeptides are produced by A. Hernandez-Garcia et al. The polypeptide consists of a very long hydrophilic block and a very short cationic block. Polymers containing cationic blocks are widely investigated as non-viral gene transfer agents. These polymers form very heterodisperse complexes with DNA, both in terms of shape and size, which usually contain multiple DNA molecules. In contrast, the diblock polypeptides developed on page 3491 form equilibrium complexes with a single DNA molecule that is uniformly coated by the polypeptide. The coating increases the stiffness and diameter of the DNA molecule such that the final complexes resemble linear viruses. This diblock polypeptide is a convenient and promising scaffold for further functionalization as a new type of nonviral gene transfer agent.