Very short-lived and stable mRNAs from resting human lymphocytes.

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Abstract
The kinetics of degradation of newly synthesized cytoplasmic poly(A)-bearing RNA have been examined in resting human lymphocytes. Two classes were identified, a very labile component with a half-life of less than 17 min and a stable component which remains apparently undiminished during 24 hr of observation. Both classes have molecular weights between 2.5 and 3.5 x 10(5) but the stable material has a narrower size distribution and a slightly lower average molecular weight than the short-lived component. The fate of stable RNA synthesized in the resting cell was also examined after growth stimulation with phytohemagglutinin after 2 and 6 hr of treatment. No transfer of stable material into the labile pool could be discerned; the amount of stable material remained constant. The existence of two species of mRNAs with different lifetimes in animal cells provides a potential means for regulation of protein synthesis by controlling the supply of specific messages. Furthermore, such a short-lived mRNA species may explain the observed disparity between the amount of poly(A)-bearing heterogeneous RNA produced in the nucleus and the amount of mature message found in the cytoplasm.