Determinants that contribute to cytoplasmic stability of human c-fos and beta-globin mRNAs are located at several sites in each mRNA.

We have analyzed the contributions to cytoplasmic stability in an mRNA species with a very short half-life (human c-fos) and an mRNA species with a very long half-life (human beta-globin). When the human c-fos promoter was used to drive the expression of human c-fos, beta-globin, and chimeric DNAs between c-fos and beta-globin in transfected cells, a pulse of mRNA synthesis was obtained following induction of transcription by refeeding quiescent cells with medium containing 15% calf serum. The mRNA half-life was determined by using Northern (RNA) blot analysis of mRNAs prepared at various times following the pulse of transcription. Under these conditions human c-fos mRNA exhibited a half-life of 6.6 min and human beta-globin mRNA exhibited a half-life of 17.5 h. Replacement of the 3' end of the c-fos mRNA with the 3' end of the beta-globin mRNA increased the half-life of the resultant RNA from 6.6 to 34 min. The reciprocal chimera had a half-life of 34.6 min compared with the 17.5-h half-life of beta-globin mRNA. These results suggest that sequences which make a major contribution to mRNA stability reside in the 3' end of either or both molecules. A chimera in which the 5' untranslated region of globin was replaced by part of the 5' untranslated region of fos led to destabilization of the encoded mRNA. This construct produced an mRNA with a half-life of 6.8 h instead of the 17.5-h half-life of globin. This result suggests that additional determinants of stability reside in the 5' end of these mRNA molecules. Substitution of part of the 5' untranslated region of fos by the 5' untranslated region of beta-globin yielded an mRNA with stability similar to fos mRNA. These results suggest that interactions among sequences within each mRNA contribute to the stability of the respective molecules.