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A clone of cells derived from a continuous line of cat cells (CCC) spontaneously produced an RNA C-type virus (CCC virus) which did not have the groupspecific antigen of the standard strains of feline leukemia viruses but did have that of the RD-114 virus. Single-hit infection of a virus yielding CCC cell with only the feline leukemia virus pseudotype of murine sarcoma virus [MSV(FeLV) ] resulted in the release of a pseudotype of MSV coated with the CCC virus envelope. Host range, transmission of virus, helper functions, interference properties, and specific neutralization showed that the CCC and the RD-114 isolates as well as their respective MSV pseudotypes are closely similar if not identical. Parental, virus-negative cells frozen before the existence of RD-114 were chemically induced to yield CCC-like virus de novo. Infection of susceptible human cells with the chemically induced virus resulted in interference with the CCC virus pseudotype of MSV but not with the FeLV pseudotype of MSV.

Small numbers of virus-like particles were observed by electron microscopy in each of two cloned lines of 3T3 cells transformed by murine sarcoma virus, even though these lines were free of detectable quantities of infectious leukemia and sarcoma virus. The morphology and occurrence of the particles were identical to those of the murine leukemia-sarcoma group. Moreover, the particles incorporated uridine and had a buoyant density of 1.16 g/ml in sucrose gradients. No evidence of sarcoma or leukemia virus infectivity was associated with the particles in cells of several susceptible species under various conditions, including both cosedimentation with leukemia virus and infection in the presence of inactivated Sendai virus. The particles may represent a form of murine sarcoma virus deficient' in one or more of the viral components necessary for infectivity.Several continuous lines of mouse embryo cells are susceptible to transformation and focus formation by murine sarcoma virus (MSV) (1, 2). Titration patterns of MSV in various isolates of mouse 3T3 cells indicate that focus formation in monolayer cultures under the usual assay conditions is dependent on dual infection by MSV and a murine leukemia virus (MuLV), which acts as a "helper" (1, 2). Thus, the behavior of MSV in mouse 3T3 cells, under certain culture conditions, is identical to that originally reported for MSV focus formation in mouse embryo cells (3). However, when culture methods are used that permit the multiplication of single transformed cells, while restricting reinfection of cells with progeny virus, both cell transformation and focus formation by MSV occur in the absence of MuLV "helper" virus and the properties of 3T3 cells infected with MSV alone can be examined (2,4).Growth of cells in semisolid agar suspension cultures is one such selective procedure that favors the multiplication of transformed cells and, at the same time, restricts virus spread (5). When 3T3 cells are infected with the Moloney isolate of MSV and plated as suspension cultures in semisolid agar, colonies of transformed cells can be seen after a suitable incubation period (2). The quantitative aspects of colony formation in this system indicate that cell transformation depends only on infection with MSV and occurs independently of infection with MuLV "helper" virus. Indeed, certain lines of MSV-transformed cells isolated from individual semisolid agar colonies contain a rescuable MSV genome in the absence of leukemia virus replication and have been designated "sarcoma-positive, leukemia-negative (S+L-)" (2). S+L-cells do not contain detectable quantities of focus-forming MSV unless superinfected with MuLV, after which both MSV and progeny MuLV are readily recovered (2). Transformation of mouse cells by MSV, therefore, does not require the replication of MuLV, and the "helper" activity of MuLV must involve either a quantitative or a qualitative effect on MSV replication.In addition to semisolid agar suspension cultures, monolayer cultures of 3T3 cells have also been us...

Annealing experiments on membrane filters were carried out with deoxyribonucleic acids (DNA) from selected strains of the nomen-species of Pseudomonas, Actinobacillus, Chromobacteriwn, and Micrococcus, with the use of DNA of Pseudomonas pseudomallei and Actinobacillus mallei as reference materials. Under the usual conditions employed in these experiments, the results were not quantitatively reproducible. Incorporation of dimethylsulfoxide (DMSO) into the incubation medium greatly increased differences in comparative binding. DNA binding in agar matrices was examined in the presence and absence of DMSO at various incubation temperatures. It was found that the greatest specificity, stability, and total binding for DNA containing high amounts of guanine and cytosine occurred in the presence of DMSO. Under the most stringent annealing conditions permitted in agar, DNA species from P. pseudomallei and A. mallei in the presence of DMSO demonstrated interspecific relative bindings of 76 to 86% when compared to the homologous reactions. The thermal elution midpoints (Em) of these duplexed interspecific DNA species were quite close to the homologous Em values. The relative bindings of P. multivorans DNA types to either reference DNA ranged between 6 to 27%, and the Em values were 4 to 7 C less than those for the homologous reactions. were extracted from these organisms and characterized by composition and homologous and heterologous annealing abilities.

A 60,000-dalton polypeptide (p60) has been identified in the feline leukemia virus (FeLV) pseudotype of Moloney sarcoma virus [MSV(FeLV)