The peptide product of a 5' leader cistron in the beta 2 adrenergic receptor mRNA inhibits receptor synthesis.

The 5' leader region of mammalian beta 2 adrenergic receptor messenger RNAs (mRNA) have a short open reading frame (sORF) preceding the receptor cistron. Mutational inactivation of the sORF start codon increased beta 2 receptor expression and translation 1.9-fold from beta 2 receptor genes transfected into COS-7 cells. sORF inactivation also increased receptor synthesis 2.4-fold in a cell-free expression system that synthesizes functional beta 2 receptor in vitro. Translational initiation at the sORF was demonstrated both in vitro and in transfected COS-7 cells using an epitope-tagged fusion protein. Using the fusion protein as a reporter for initiation at the sORF shows that 5' leader mutations which increase translation of the sORF decrease receptor translation. Mutation analysis of the 5' leader region and peptide coding sequences suggests the peptide itself inhibits beta 2 receptor expression. Consistent with this hypothesis, a synthetic peptide corresponding to the peptide encoded by the beta 2 receptor sORF potently inhibits translation in vitro. Our results suggest that a nonoverlapping cistron in the beta 2 receptor mRNA 5' leader region is translated and the resulting peptide inhibits receptor translation.