THE MATURATION OF WESTERN EQUINE ENCEPHALOMYELITIS VIRUS AND ITS RELEASE FROM CHICK EMBRYO CELLS IN SUSPENSION

Experiments are presented in which the plaque assay technique was used to study the intracellular appearance and release of Western equine encephalomyelitis virus in suspensions of infected chick embryo fibroblasts. No intracellular virus could be found during the 1st hour after adsorption in spite of the fact that more than 1014 cells per ml. proved to be infected. This is taken to indicate that the infecting particle loses its infectivity upon entering a susceptible cell. The first progeny virus was detectable in the cells between 1 and 2 hours after infection, and it increased in amount exponentially during the following 3 hours. The released virus as measured in the supernatant fluid increased at the same rate as the intracellular virus but exceeded it in amount by a factor of about twenty at all times during the period of exponential increase. More than 100 particles were spontaneously released from each cell, by the end of the period of exponential increase, yet the maximum number of intracellular infective particles at any instant during this period was never more than an average of from 4 to 10 per cell. Calculations based on these findings indicate that, on the average, a virus particle is released from the cell within 1 minute after it gains the property of infectiousness

Homological interference by ultraviolet inactivated virus in Newcastle disease virus

The present study concerns a quantitative analysis of the interference between the irradiated and the active Newcastle disease virus. The inactivated particles adsorb to the surface of the cells and do not proceed any further. This union induces surface changes which make it impossible for a superinfecting active particle to penetrate into the host cell and to initiate the production of new virus. The more UVI particles that are adsorbed, the faster the interfering reaction occurs. In 50 per cent of the cells, however, interference is not complete; these cells can be superinfected provided the multiplicity of the superinfecting virus is high. The effect is equivalent to having on the average four per cent of the total surface of the cell unaffected by the changes induced by the inactivated virus. The interfering reaction is dependent at all times upon the presence of the unmodified UYI particles at the critical sites - exposure of the interfered cells to specific anti-NDV serum eliminates interference. However, in 50 per cent of the cells interference becomes irreversible 30 minutes after the attachment of UVI virus. Whether this irreversible interference involves more profound cellular changes or depends upon the physiological state of the cells at the time of infection is at present unknown. Eventually, the union between UVI virus and cellular site is broken with the subsequent return of the cell to susceptibility to infection. This loss of resistance occurs spontaneously from 26 to 60 hours after exclusion has been induced. The superinfecting virus which does not initiate infection is destroyed after its adsorption to the lung cell. A cell where interference has been removed after superinfection with active virus must be infected a second time in order to yield progeny virus

Enhanced activity of cloned hamster TERT gene promoter in transformed cells

In 7,12-dimethylbenz[a]anthracene-treated hamster pouch epithelial cells, telomerase activity increased within 1 week of treatment and reached a 6–7-fold increase within 3 weeks. To investigate this phenomenon, we have cloned and sequenced the hamster telomerase catalytic subunit (hamTERT) promoter. Transient transfection with different genomic segments upstream of the ATG translation initiation codon linked to the luciferase reporter gene mapped the core promoter within a 250 bp region. Three major transcription initiation sites and several minor sites were found between −42 and −140 bp relative to the ATG site. Like the human and murine TERT promoters, the hamTERT promoter lacks TATA and CAT boxes and all three promoters share similar regulatory factor binding sites. DNase I footprint analysis revealed six protected regions which contain sequences homologous with known transcription factor binding sites. Three protein binding regions (I, II, and III) were essential for the promoter activity. Regions I and III bound to Sp1 and Sp3 transcriptional factors, whereas region II bound to an unknown factor. Transient transfection of a promoter-luciferase plasmid into Drosophila SL2 cells showed that Sp1 and Sp3 regulated the hamster TERT promoter in a concentration-dependent and synergistic manner. Telomerase activity showed a 2–4-fold and 8–10-fold increase in immortalized cells and tumor cells, respectively, but hamTERT expression was only increased 1.7-fold and 2.4-fold, respectively, in the same cells