No abstract

Pf1 is a filamentous, single-stranded DNA virus that has Pseudomonas aeruginosa (strain K) as host. It is the longest of the filamentous bacterial viruses, and the DNA within it has the most extended conformation known. Pf1 virus cannot infect Escherichia coli (strain MM294) cells, but when these cells are transfected with the double-stranded replicative form of Pf1 DNA (RF DNA, 7.35 kb), they export low levels of infectious particles that create plaques on lawns of P. aeruginosa. Several different structural species, at least two of which are infectious, are exported. One of them, called Epf1, has virtually the same structure as Pf1, but the amount of Epf1 exported by E. coli is 10(4) lower than the amount of Pf1 exported by P. aeruginosa. The results imply that host factors affect not only the efficiency of virus assembly and export, but also the actual structures of the species exported.

Inovirus C2 is 1295 nm long and 6.8 nm in diameter, and its mass is 24 million Da. Its genome is a topologically circular, single-stranded DNA molecule of 8100 nucleotides. The DNA is packed in the virion as two antiparallel strands, with a rise per nucleotide in each strand of 3.2 A; it can be assigned spectroscopic properties like those of base-stacked, right-handed, double-stranded DNA. The stoichiometric ratio (n/s) of nucleotides to subunits of the major coat protein is close to 2. The protein subunit contains 52 amino acids, and the DNA sequence of its gene does not encode a signal peptide. The protein conformation in the virion is helical, mostly alpha-helix with perhaps some 3(10)-helix. The amino acid sequence of the DNA interaction domain of the subunit is unique among Inovirus species. On the basis of its coat protein sequence and available theories of helical symmetry in such structures, C2 appears to be either an unusual member of filamentous virus symmetry class II or the defining member of a new symmetry class.