Naturally elaborated membrane bleb material is frequently observed in cultures of Neisseria gonorrhoeae. This material was purified and analyzed for protein, lipopolysaccharide, and nucleic acid content antigen, and lipopolysaccharide (LPS) (8). Preliminary characterizations showed that significant quantities of naturally elaborated membrane blebs are recoverable from broth culture supernatants of N. gonorrhoeae. Although this finding suggests active formation of these vesicles by gonococci (8), the physiological role of the vesicles is obscure.Purified blebs equilibrate into two fractions, BI and BII, with respective densities of 1.12 and 1.30, by sucrose density gradient centrifugation (8). Because constituents unique to BI or BII might account for the density difference, we first considered whether nucleic acids were associated with bleb fractions. After finding plasmids, linear DNA, and RNA associated with blebs, we examined whether the DNA found in blebs could be incorporated and expressed by recipient gonococci.The results showed that plasmids are sequestered within outer membrane-derived BIT vesicles and resist exhaustive DNase digestion. In addition, wild-type recipient gonococci incorporated and expressed penicillinase-specifying plasmids associated with blebs when incubated in suspensions of blebs and DNase.

The genetics of spirochetes, a division of eubacteria, has been little studied. Double-stranded linear plasmids were found in Borrelia burgdorferi, the agent of Lyme disease. A 49-kilobase linear plasmid contained the ospA and ospB genes, which encode the major outer membrane proteins of strain B31. Molecules of the 49-kilobase plasmid rapidly reannealed after alkaline denaturation; rapid renaturation was prevented if the 49-kilobase plasmids were first treated with S1 nuclease. When denatured plasmid molecules were examined directly, single-stranded circles of approximately 100-kilobase circumference were seen. These studies provide direct visual evidence that the linear plasmids have covalently closed ends. This form of DNA occurs in some animal viruses, but it has not heretofore been described in prokaryotic organisms.

To date no nucleic acid has been found in the purified infectious agent which causes the spongiform encephalopathy known as scrapie. In an attempt to identify a unique scrapie virus-associated messenger RNA in tissues of infected animals, we have synthesized an oligonucleotide probe complementary to the mRNA sequence corresponding to the amino-acid sequence of the prion protein, PrP27-30 (ref. 1). We report here that, with this probe, a complementary DNA clone representing PrP27-30 was obtained from scrapie-infected mouse brain; the DNA sequence of this clone could be translated into a protein that matches exactly the published sequence of PrP27-30. The cDNA clone hybridized to a single 2.4-2.5-kilobase (kb) mRNA from both normal and scrapie-infected brain. Thus, the PrP27-30 mRNA is not uniquely associated with scrapie infectivity, suggesting that PrP27-30 may be a normal component of mouse and hamster brain.