Terminal sequences do not contain the rate-limiting decay determinants of E. coli cat mRNA

The mechanism of E. coli chloramphenicol acetyltransferase (cat) mRNA decay was investigated. Alteration of the 5' untranslated terminus does not appear to have an effect on the turnover rate of the mRNA. Similarly, changes at the 3' terminus of the message, including the addition of a stable stem and loop structure, do not affect the half-life of the message. The data suggest that 5' and 3' terminal untranslated sequences do not contain the rate-limiting determinants for cat message decay. Decay rates for various segments of the cat mRNA were measured and indicate that all regions of the message have similar stabilities. The current model of cat mRNA degradation involves a rate-limiting endonucleolytic decay event that occurs internal to the message followed by degradation of the cleavage products.