These efforts include protein capsids and liposomes. Researchers have continued to experiment with pseudotyping by creating strains with hybrid capsids. The head capsids, constructed separately, will spontaneously assemble with the tails. The "T"-number is representative of the size and complexity of the capsids. This realm is recognized for its use of vertically-folded jelly roll capsids. Another effective approach is to deliver transposons through viral capsids. Orthobornavirions are enveloped, with spherical geometries and helical capsids. They show electron dense glycoproteins and viral capsids. The escape hypothesis did not explain the complex capsids and other structures on virus particles. The packaging of bacteriophage DNA into phage capsids has low fidelity. Retroviruses carry specific proteins within their capsids, which typically associate with the RNA genome. Immature capsids are formed from coiled DNA. VP90 is proteolytically cleaved during packaging and produces immature capsids made of VP70. All known eukaryotic ssDNA viruses have icosahedral capsids. Capsids are broadly classified according to their structure.