Volume 70, no. 3, p. 1279-1286, 2002. Subsequent to the publication of this article, we discovered that additional preparations of cloned Shiga toxin 2 (Stx2) B subunit lacked apoptogenic activity in Ramos Burkitt's lymphoma B cells. After exhaustive biological and biochemical characterization, we discovered that the Stx2 B subunit preparations used in our study contained previously undetected Stx2 holotoxin. Since this contaminating Stx2 holotoxin was likely responsible for the apoptogenic activity we attributed to the Stx2 B subunit in this article, we retract the conclusion that the Stx2 B subunit, absent any A subunit activity, initiated apoptosis in Ramos cells. This new finding does not alter our conclusions related to the lack of apoptogenic activity in the Stx1 B subunit preparation or the protective effect of Z-VAD-fmk on protein biosynthesis in the Stx2 B subunit-treated Ramos cells.
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