- Volume 49, Issue 2, 1980

Moloney-murine sarcoma virus (Moloney-MSV) and simian virus 40 (SV40) were found to infect successfully pure cultures of epithelial cells established from mouse liver and mammary tissue. MSV infection resulted in transient morphological foci with persistent production of infectious virus. SV40 infection produced detectable levels of virus-specific T antigen in the cells but morphological transformants were not observed.

Pre-treatment of L cells with 750 units/ml of mouse interferon depressed the yield of interferon when the cells were treated with Newcastle disease virus (NDV). The refractory state persisted for more than 5 days. Nucleated fragments (karyoplasts) obtained by cytochalasin B-induced enucleation were made from such interferon pre-treated cells; cells reconstituted from these karyoplasts produced less interferon in response to NDV than did cells reconstituted from karyoplasts derived from untreated cells. The source of the enucleated cytoplasm (cytoplasts) used in the cellular reconstitutions did not affect the yields of interferon.

Tissue from symptom-bearing young leaves of Gynura aurantiaca plants systemically infected with citrus exocortis viroid (CEV) was investigated with the electron microscope. It was found that, in contrast to a previous report, the appearance of paramural bodies or plasmalemmasomes cannot be considered to be the primary c.p.e. in G. aurantiaca because these structures are also present at the same frequency in healthy control plants. The plasmalemmasomes in healthy tissue, characterized by vesicular or tubular internal structures, are found at different developmental stages and in the process of spreading between the plasmalemma and cell wall of developing young cells. The viroid-specific cytopathic changes are alterations of the plasmalemmasomes themselves, which may make it difficult to relate them to the corresponding normal structures. The malformed plasmalemmasomes were consistently found in association with the extremely distorted cell walls characteristic of viroid-infected tissue; spreading of plasmalemmasomes was not observed. These findings indicate an intimate functional relationship between plasmalemmasomes and cell wall formation which is disturbed as a consequence of viroid infection.

X-ray diffraction studies of oriented specimens of potato virus X, and optical diffraction from electron micrographs of individual particles, are consistent with a helical structure which repeats in eight turns of the helix as proposed by Horne et al., (1975). The studies further suggest that there are 8q + 7 protein subunits in the repeat period, and that the probable number of subunits in eight turns is 71.