High-resolution analysis of gro alpha mRNA poly(A) shortening: regulation by interleukin-1 beta.

We have previously shown that destabilization of gro alpha mRNA is associated with poly(A) shortening. In this study, we used high-resolution Northern blots to determine the rate and extent of gro alpha mRNA poly(A) shortening. gro alpha mRNA was found to undergo complete deadenylation within 2 h following withdrawal of IL-1. However, the process was not uniform: at 1 h following IL-1 withdrawal, gro alpha mRNA poly(A) lengths ranged from 0 to 180 nucleotides. There was an accumulation of deadenylated gro alpha mRNA which suggested that there may be another step before the mRNA is destroyed. Cycloheximide was found to block gro alpha mRNA degradation at the level of poly(A) shortening. Northern blots revealed a previously unrecognized periodic distribution of poly(A) lengths that was consistent with endonucleolytic cleavage between complexes of poly(A)-binding protein. The findings indicate that the degradation pathway of gro alpha mRNA is a slower version of the c-fos mRNA model, with the important additional feature that deadenylation and degradation are subject to physiologic regulation. This study provides a detailed picture of gro alpha mRNA poly(A) shortening and establishes a basis for further investigation of the mechanism by which IL-1 stabilizes specific mRNAs.