A COMPARISON OF THE CHANGES IN FINE STRUCTURE OF L CELLS DURING SINGLE CYCLES OF VIRAL MULTIPLICATION, FOLLOWING THEIR INFECTION WITH THE VIRUSES OF MENGO AND ENCEPHALOMYOCARDITIS

The virus of encephalomyocarditis (EMC), examined by the negative-contrast method, is indistinguishable from the serologically related Mengovirus. The particles are 270 to 280 A in diameter. The surface of EMC is composed of an undetermined number of subunits. Frequent sampling of infected cells was carried out throughout one-step cycles of viral multiplication to observe cytopathic changes occurring in L cells infected by these two related RNA viruses. EMC and Mengovirus, which multiply at equal rates, in most respects elicit similar alterations in cell fine structure. Rearrangement and changes in nuclear material accompanied by formation of small vesicles in the centrosphere region commence at 4 to 6 hours after infection. Thereafter a progressive degeneration of the nucleus and vesiculation of the cytoplasm are observed up to 18 to 20 hours. Increased numbers of small dense granules, indistinguishable from ribonucleoprotein particles, appear in the cytoplasm between 8 and 14 hours after infection. L cells infected with Mengovirus become permeable to Erythrocin more slowly than those infected with EMC. Only in the case of Mengovirus infection are large aggregates of dense material first observed in the cytoplasm at 8 hours, followed by the appearance of crystals probably composed of Mengovirus particles, at 12 hours. Differences in the rates of cell permeability after infection with EMC and Mengovirus are discussed in relation to formation of virus crystals and plaque-type mutants.     

Selective Inhibition of Reovirus Ribonucleic Acid Synthesis by Cycloheximide

Cycloheximide, at a concentration of 10 mug/ml, rapidly blocked protein synthesis in L cells infected with reovirus. When the drug was added before 5 hr postinfection, synthesis of both single- and double-stranded varieties of virus-specific ribonucleic acid (RNA), which normally commences between 6 and 7 hr after infection, was blocked. When the cycloheximide was added at 9 hr after infection, uptake of uridine-H(3) into RNA, for the succeeding 6 hr at least, was similar to that of an infected culture without the drug. This latter uptake of uridine-H(3) in the presence of cycloheximide was largely into single-stranded RNA, since double-stranded RNA synthesis was rapidly and markedly inhibited by the cycloheximide. Single-stranded RNA formed in the presence of cycloheximide was found not to be a precursor of viral progeny, double-stranded RNA. Synthesis of double-stranded RNA in the infected cell probably requires prior synthesis of a new protein, which has a rapid rate of turnover. The possibility that formation of single-stranded RNA is preceded by synthesis of a second new protein is discussed.     

THALASSIOMYCETES II. NEW GENERA AND SPECIES OF DEUTEROMYCETES

Meyers , Samuel P. (U. Miami, Coral Gables, Fla.) and Royall T. Moore . Thalassiomycetes II. New genera and species of Deuteromycetes. Amer. Jour. Bot. 47(5) : 345-349. Illus. 1960.–On the basis of taxonomic studies, 3 new monotypic thalassic genera are erected. These are: Cirrenalia, type C. macrocephala (=Helicoma macrocephala Kohlmeyer) ; Cremasteria, type C. cymatilis; Culcitalna, type C. achraspora . Also described is a new species of Humicola, H. alopallonella, which constitutes the first report of this genus from the marine environment.