Increased efficiency of translation of ornithine decarboxylase mRNA in
mitogen-activated lymphocytes
Michael W. WHITE, Takaaki KAMEJI, Anthony E. PEGG and David R. MORRIS
Ornithine decarboxylase (ODC) mRNA was elevated nine-fold by 6 h following
concanavalin A (ConA) stimulation of bovine lymphocytes. Comparison of
the increases in ODC mRNA and ODC activity revealed a five-fold discrepancy,
which is consistent with a change in efficiency of translation of ODC mRNA.
In resting cells, 45% of the total ODC mRNA was associated with particles
sedimenting at about 40S, and therefore was not translated. The untranslated
ODC mRNA in resting cells could be completely shifted into polysomes by
a 5-min treatment of the cells with appropriate concentrations of eycloheximide.
In activated cells, the proportion of ODC mRNA in untranslated material
was reduced to 18%. This shift in distribution of ODC mRNA occurred between
6 h and 12 h following mitogen stimulation with no increase in the cellular
level of this message. The rate of synthesis of ODC protein was found in
increase two-fold between 6 h and 12 h, paralleling the increase in the
amount of ODC mRNA associated with polysomes. Thus, in this time frame,
a decrease in the amount of untranslated ODC mRNA with a corresponding
increase in the amount associated with polysomes leads to an increase in
the biosynthesis of ODC with no change in the cellular level of the message.
These changes in translational efficiency were not observed with actin
mRNA.