Only a few archaeal viruses have been subjected to detailed structural analyses. Major obstacles have been the extreme conditions such as high salinity or temperature needed for the propagation of these viruses. In addition, unusual morphotypes of many archaeal viruses have made it difficult to obtain further information on virion architectures. We used controlled virion dissociation to reveal the structural organization of Halorubrum pleomorphic virus 1 (HRPV-1) infecting an extremely halophilic archaeal host. The single-stranded DNA genome is enclosed in a pleomorphic membrane vesicle without detected nucleoproteins. VP4, the larger major structural protein of HRPV-1, forms glycosylated spikes on the virion surface and VP3, the smaller major structural protein, resides on the inner surface of the membrane vesicle. Together, these proteins organize the structure of the membrane vesicle. Quantitative lipid comparison of HRPV-1 and its host Halorubrum sp. revealed that HRPV-1 acquires lipids nonselectively from the host cell membrane, which is typical of pleomorphic enveloped viruses.
