Wyckoff, E.E., Croall, D.E., Ehrenfeld, E. 1990. The p220 component of eukaryotic initiation factor 4F is a substrate for multiple calcium-dependent enzymes. Biochemistry. 29(43):10055-10061.
Eukaryotic initiation factor 4F (eIF-4F) is a multisubunit protein that
functions in the first step of the binding of capped mRNAs to the small
ribosomal subunit. Its largest polypeptide component, p220, is cleaved following
poliovirus infection. This is thought to inactivate eIF-4F function, thereby
preventing cap-dependent initiation of translation of cellular mRNAs. In this
report, we show that p220 in extracts of uninfected HeLa cells is specifically
lost in the presence of calcium. The responsible activities have been partially
purified and identified as the calcium-dependent, neutral, cysteine proteases
calpains I and II. In addition, a third calcium-dependent activity was resolved
from the calpains and also results in the loss of p220. This activity has
properties similar to a transglutaminase and copurifies with tissue
transglutaminase through several chromatographic steps. None of these
calcium-dependent activities appears to mediate p220 cleavage in
poliovirus-infected cells.
