FIG. 1.

Comparison of Stx2 and StxA1 mutant enzymatic and antiviral activities. Enzymatic and antiviral activities of Stx2, three mutant toxins, and StxA1 were compared in protein synthesis (A) and cell proliferation (B) inhibition assays. Rabbit reticulocyte lysates were preincubated with various amounts of StxA1, Stx2 holotoxin, A-B association mutant (StxA₁1), enzymatic mutant (E167D), or cell-trafficking mutant (A231G-D234E) or with no toxin, and these lysates were then used in a luciferase protein synthesis assay. Toxin enzymatic activity was expressed as a percentage of that of the control and was calculated by dividing the amount of luciferase made by lysates incubated with toxin by the amount of luciferase made by lysates without toxin. PBMC from BLV-positive cattle were cultured for 72 h with various amounts of StxA1 or Stx2 holotoxin or with no toxin. Antiviral activity was expressed as a percentage of that of the control and was calculated by dividing the amounts of [³H]thymidine incorporated by PBMC cultured with toxins by the amounts incorporated by PBMC cultured without toxin. Data are means ± SE from two experiments performed in duplicate (protein synthesis inhibition) or four experiments performed in quadruplicate (PBMC proliferation).