PubMed · 5345363
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R Oliver. 1969. Dose-rate effects associated with sub-lethal damage.. https://pubmed.ncbi.nlm.nih.gov/5345363/
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We show that the typical "nonclassical" activator, which comprises a fusion protein bearing a component of the transcriptional machinery fused to a DNA-binding domain, activates transcription in mammalian cells only weakly when tested with an array of promoters. However, as found in analogous "artificial recruitment" experiments performed in yeast, these activators work synergistically with "classical" activators. The effect of the classical activator in such experiments requires that it be tethered to DNA, a requirement that cannot be overcome by expression of that classical activator at high levels. The effect of the one nonclassical activator that does elicit significant levels of transcription when working alone (i.e., that bearing TATA box-binding protein) is strongly influenced by promoter architecture. The results, consistent with those of analogous experiments in yeast [see the accompanying paper: Gaudreau, L., Keaveney, M., Nevado, J., Zaman, Z., Bryant, G. O., Struhl, K. & Ptashne, M. (1999) Proc. Natl. Acad. Sci. USA 96, 2668-2673], suggest that classical activators, presumably by virtue of their abilities to interact with multiple targets, have a functional flexibility that nonclassical activators lack.
Rhinoviruses are epidemiologically connected to the majority of acute asthma exacerbations; however, their ability to infect and replicate in the lower airways is disputed. A frequent argument against this possibility involves the temperature preference for rhinovirus replication, generally accepted to be 33 degrees C, the temperature of the nasal passages. However, this argument is based on studies with a single rhinovirus serotype. In this study, differences in temperature preferences were evaluated between several serotypes and relative titers were determined than can be achieved at upper and lower airway temperatures. Rhinovirus serotypes 1b, 2, 7, 9, 14, 16, 41, and 70 were titrated in Ohio-HeLa cell cultures at either 33 degrees C or 37 degrees C. Possible selection by culture temperature was examined by continuous culture at 33 degrees C and 37 degrees C for 2-4 passages and subsequent titration at both temperatures. Finally, nasal aspirate samples derived from patients with wild-type rhinoviral common colds were cultured at 33 degrees C and 37 degrees C and RT-PCR was used to assess rhinovirus replication at each temperature. The majority of the serotypes and wild-type viruses replicated slightly better at 33 degrees C than at 37 degrees C. However, titers achieved after one or more replicative cycles at 37 degrees C were still high enough to initiate infection. Furthermore, in some instances equal or even better replication was observed at 37 degrees C. It is concluded that temperature preferences may vary between rhinoviruses and are not likely to be a prohibitive factor for infection of the lower airways.
Several mutants of the Mahoney strain of poliovirus type 1 have been generated by introducing mutations into the stem-loop II (SLII) structure within the internal ribosomal entry site (IRES). Four of these mutants (SLII-1, -4, -5 and -6 mutants) have been characterized previously and are host-range mutants that replicate well in human HeLa cells but not in mouse cells. Two deletion mutants, SLII-2 and SLII-3, were non-viable, even in HeLa cells. It is now reported that SLII-2 was defective in genome RNA synthesis and viral protein synthesis, while SLII-3 was defective only in viral protein synthesis. These results indicate that the SLII region contains a cis-element for RNA replication as well as for IRES-dependent translation and that these two functions lie at the same sites within the SLII region. The host cellular factors that interacted with wild-type SLII and mutant SLII-2 and SLII-3 RNAs were different, suggesting that different host-factor binding regulates expression of mutant phenotypes.