SUMMARYComplementary single-stranded RNAs from three independent VSV defective interfering particle (DI) sources examined can anneal and give rise to monomeric and multimeric circular and linear double-stranded structures observable by electron microscopy under aqueous conditions. When the RNA from the shortest of these DI is spread from 8o % formamide solutions, as many as 32 ~o of the molecules are circular, suggesting that the single-stranded RNAs contain inverted complementary terminal sequences. This is strongly supported by the isolation of the putative terminal sequences which rapidly become RNase resistant basepaired structures after melting and quick-cooling the RNA. RNase digestion yields a major and a minor component, 6o to 70 and I35 to I7o nucleotides long respectively. Snap-back DI RNAs also contain inverted complementary sequences at both ends of the plus and minus strands of the duplexes since nicking these at the ends gives rise to double-stranded molecules which can form monomeric and multimeric circular and linear molecules. Thus, snap-back molecules most likely contain a covalent linkage between or near complementary terminal sequences on the two complementary strands as schematically shown in Fig. 5 D.

SUMMARYVSV defective interfering particles of various sizes and from several independent sources frequently contain plus and minus strand RNA. In many cases some of the complementary strands are covalently linked as snap-back molecules. Infectious particles on the other hand package little or no plus strands. Snap-back molecules from the three different sources examined so far vary in size but appear to conform to the same overall linear duplex structure with cross-links at the ends only. They each contain a base sequence which is a subset of the next larger one and appear to correspond to unique sequences in the L cistron of the genome. Possible origins for these snap-back molecules are discussed.

SUMMARYThe infection of cultured cells of the fruit fly Drosophila melanogaster (Schneider) with vesicular stomatitis virus (VSV) led to the establishment of persistent noncytocidal infection. After weeks or months of persistent infection many VSV variants or mutants were detected all of which showed increased capacity for growth in these insect cells. We present a preliminary characterization of these viruses arising in the Drosophila cells.

Herpes simplex virus survived in Virocult transport tubes and had a half-life of 3.5 days at 2°C and 2.75 days at 22°C. Of 2,000 consecutive clinical specimens transported on Virocult tubes and cultured for herpes simplex virus, 448 (22.4%) were positive. Comparison of the holding times between positive and negative cultures, up to 12 days, revealed no significant loss of positive cultures with time.

In a comparative study, clinical specimens were cultured for herpes simplex virus (HSV). The presence of virus was noted by the appearance of characteristic cytopathic effect, as determined by standard direct immunofluorescence techniques, by using a direct immunoperoxidase stain for viral antigen, or by using the Selecticult-HSV (SC-HSV) stain for viral antigen. There was 100% correlation between the SC-HSV stain and immunofluorescence staining in recognizing HSV-infected cells (81 of 81 positive specimens). In comparison with observation of cytopathic effect, the SC-HSV system and conventional culture detected 93 and 78% of positive cultures at 48 h postinoculation and 76 and 32%, respectively, at 24 h. By 5 days postinoculation, SC-HSV detected 100% of the positive specimens. As compared with the direct immunoperoxidase stain, SC-HSV stain was slightly more sensitive and gave less background stain. HSV serotypes 1 and 2 were both detected by the SC-HSV stain. The Scott SC-HSV kit appears to be an effective system for the diagnosis of HSV infections.