The levels of mRNA encoding hnRNP core protein A1 have been compared in quiescent and proliferating Rat-1 embryonic fibroblasts. Northern blot hybridization analyses using probes made from an A1 cDNA clone, λHDP-182, isolated by Cobianchi et al. (J. Biol. Chem. 261:3536-2543 (1986)) indicated that three sizes of poly A+ RNAs, 1.6, 2.0, & 4.0 kb, have extensive sequence homology. The levels of all three A1 RNA species are responsive to the proliferation state of the cells. Stimulation of quiescent Rat-1 cells with serum or epidermal growth factor resulted in a 2- to 5-fold increase in the levels of each of these three RNAs that was evident after 2 hours and reached a peak after about 8 hours. Addition of the protein synthesis inhibitor, cycloheximide, along with epidermal growth factor completely blocked the upsurge in A1 RNA levels. Thus, the A1 RNA species are not primary transcriptional targets of epidermal growth factor but do show an induction pattern similar to mRNAs encoding some glycolytic enzymes.
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