Perturbation of the switch‐on of transcriptase activity in intermediate subviral particles from reovirus

Abstract

Intermediate subviral particles (ISVP) derived from reovirus represent a simple model system for the switch-on of transcriptase function. In such particles the endogenous transcriptase is present in a switched-off form, one step removed from the switched-on state. Switch-on of transcriptase function is an active process in this system and can be triggered by K+ions. A variety of agents which affect gene expression in cells were tested for an effect on switch-on in ISVP. Marked effects on switch-on in ISVP were observed with a diverse group of test agents, including DMSO and other solvents, BUdR, TdR, caffeine, theophylline, and temperature. The correlation in response between ISVP and cells suggests that the ISVP system may be useful as a model for studying the biochemical mechanisms underlying the perturbative effects of such agents on gene expression in cells.

Strategy for Nonenveloped Virus Entry: a Hydrophobic Conformer of the Reovirus Membrane Penetration Protein μ1 Mediates Membrane Disruption

“…These observations strongly suggest that the outer capsid in general, and protein 1 in particular, play a role in regulating the activity of the core-associated transcriptases. Other experiments showed that incubation of ISVPs with K ϩ or Cs ϩ ions at 37°C is sufficient for derepression of transcriptase activity and that proteolytic removal of 1 from viral particles is not required (9,12,23,57). In the present study, we found that incubation of ISVPs with Cs ϩ ions accelerates, in concert, both conformational change in 1 (Fig.…”

“…T3D ISVPs are proteolytically digested to cores more efficiently when incubated with K ϩ , Rb ϩ , or Cs ϩ ions in place of Na ϩ or Li ϩ ions (9, 11). Since differences among viral strains in the susceptibility of ISVPs to undergo proteolytic digestion to cores are genetically determined by M2, encoding 1 (10), these results suggest that K ϩ , Rb ϩ , and Cs ϩ ions allow more efficient conversion of ISVPs to cores by increasing the capacity of 1 to undergo protease digestion (12,13). Based on these previous findings, we speculated that the propensity of T1L 1 to acquire a protease-sensitive conformation when ISVPs are incubated with RBCs may be enhanced by inclusion of K ϩ , Rb ϩ , or Cs ϩ ions in the hemolysis reaction.…”

Potential for Improving Potency and Specificity of Reovirus Oncolysis with Next-Generation Reovirus Variants

“…In ISVPs, the myristoylated µ1N fragment (residues 1–2), the δ fragment (residues 43–581) and the short C-terminal ϕ fragment remain particle-associated. Host membrane exposure promotes formation of ISVP* through conformational changes in µ1 and release of membrane-pore-forming µ1N and ϕ fragments from virus particles [ 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 ]. The importance of releasing the myristoylated µ1N fragment and ISVP* formation is demonstrated by the dramatic loss of infectivity by reovirus particles with mutations that prevent µ1 processing [ 104 , 107 ].…”