Western analyses of eIF2α phosphorylation in the strains expressing zebrafish PKR and the various vIF2α mutants revealed that vIF2α, vIF2α+26C,
vIF2α59C led to strong and comparable inhibition of eIF2α phosphorylation (Figure 5D, next to bottom panel, JNK-IN-8 lanes 2-4). Consistent with their inability to inhibit PKR G418 in vitro toxicity in yeast, high levels of eIF2α phosphorylation were observed in strains expressing the other vIF2α mutants (Figure 5D). As seen earlier, PKR was expressed at higher levels and migrated faster on SDS-PAGE when PKR toxicity and eIF2α phosphorylation were suppressed (Figure 5D, top panel). Western blot analyses using antibodies against a C-terminal Myc-epitope tag in the vIF2α constructs revealed detectable expression for only vIF2α, vIF2α+26C, and vIF2α59C. Comparable results were obtained in Western blot analyses of protein extracts from the control (-PKR) strain Omipalisib in vivo expressing these same vIF2α mutants (data not shown), indicating that both the S1 domain and the helical domain are essential for vIF2α expression and/or stability. Figure 5 Both S1 and helical domains in vIF2α are required for PKR inhibition. (A) Schematic representation of RCV-Z vIF2α constructs tested in yeast growth assays and Western blots analyses. S1 domain (red), helical domain (HD;
blue) and C-terminal domain (CTD, yellow) are represented by boxes. Numbers that follow deltas (Δ) indicate the(number of residues that were deleted from the C- or N-terminus, respectively. The extended C-terminus (26 amino acids) from ATV vIF2α was added to the C-terminus of RCV-Z vIF2α in the constructs with the +26C label. The indicated constructs were introduced into isogenic yeast strains having either an empty vector (B, J673) or a GAL-CYC1-zebrafish PKR construct (C, J944) integrated at the LEU2 locus. The indicated transformants were streaked on SC-Gal medium where expression of both PKR and the viral
proteins was induced, and incubated at 30°C for 4 days. Results shown are representative of 4 independent transformants for each plasmid. (D) Transformants Etofibrate described in panels B-C were grown in liquid SC-Gal medium for 13 hours, then whole cell extracts were obtained from equal numbers of cells and subjected to SDS-PAGE followed by immunoblot analysis. Following transfer to nitrocellulose membranes, the upper half of the blot was probed with anti-Flag tag antibodies, which detect Flag-tagged zebrafish PKR (top panel). The lower part of the blot was incubated with anti-Myc tag antibodies to detect Myc-tagged vIF2α (second panel from top), then stripped and probed with phosphospecific antibodies against Ser51 in eIF2α (eIF2α-P; third panel from top), and finally stripped again and probed with polyclonal antiserum against total yeast eIF2α (bottom panel).