Growth-related changes in specific mRNAs of cultured mouse cells

A cDNA plasmid library has been constructed from the poly(A)⁺ RNA present in BALB/c 3T3 cells after serum stimulation. Of 3,500 clones tested, approximately 0.5% contained inserts corresponding to mRNAs present at higher levels in serum-stimulated BALB/c 3T3 cell cultures than in quiescent cultures. Most of these RNA species increased 2- to 5-fold, and the kinetics of increase for various RNAs differed. One clone (28H6) hybridized to a 1-kilobase RNA species that is present at barely detectable levels in resting cells but is increased at least 15- to 29-fold after serum stimulation, reaching a maximal level coincident with the onset of DNA synthesis. This RNA was at a high level in proliferating cells but decreased rapidly as cells reached confluence. 28H6 RNA was also increased in resting cells infected with simian virus 40 or stimulated with platelet-derived growth factor.