Short-lived methylated messenger RNA in mouse kidney.

In experiments originally designed to examine selective turnover of methylated "caps" in renal mRNA, we observed that [3H]methyl label decayed from mRNA containing poly(A) with a half-life of 1-2 hr. (Caps are blocked, methylated mRNA sequences of the general structure m7GpppNm p(1 or 2)Np.). To distinguish between metabolism of short-lived mRNA and discriminate turnover of "caps", we compared residual [3H]methyl label in 5' and 3'mRNA fragments prepared from mRNA isolated during the decay period. Hydrolysis of mRNA at 0 degrees with dilute KOH before oligo(dT)-cellulose selection produced 5' mRNA fragments enriched with an alkali-resistant oligonucleotide with a -5 charge; the 3' mRNA fraction was correspondingly reduced in oligonucleotide content. Since methyl label disappeared at the same rate from both fractions, we conclude that mouse kidney contains short-lived mRNA and that the "caps" of these labile mRNAs turn over with the rest of the mRNA molecule.