Translation of poly(A)-binding protein mRNA is regulated by growth conditions.

Translational efficiency of a minor group of mRNAs is regulated by serum levels in 3T6 fibroblasts. Included within this group is the poly(A)-binding protein (PABP) mRNA. We analyzed the distribution of PABP mRNA in polysome profiles and found a large percentage of this mRNA to be translationally repressed in both actively growing (approximately 60%) and resting cells (approximately 70%). Elevated serum levels induced a distinct bimodal distribution of this mRNA between actively translated and repressed fractions. Similarly, treatment of cells with low doses of cycloheximide also generated a partial shift of repressed PABP mRNA into the actively translated fraction. In an attempt to characterize the factors which regulate PABP mRNA translation we have identified the proteins which bind to this mRNA in vitro. Sequences within the 5' untranslated region were found to be sufficient for binding of all proteins to this mRNA. We suggest that this region and the proteins associated with it may be essential for translation control of PABP mRNA.