Units of functional stability in bacteriophage messenger RNA

Abstract

The functional stabilities of the messages for seven of the nine genes of bacteriophage S13 were determined by measuring the amount of gene-specific translation at different times after the addition of rifampicin to block further initiation of transcription. Although the decay of mRNA function for each gene product tested was exponential, the functional half-lives of the mRNA were not the same for all phage genes, but fell into at least five groups: 6·2 minutes for genes B and C ; 4·4 minutes for D ;3·8 minutes for F, G and H ; 2·5 minutes for A * and 0·65 minutes for A . The overall mass-decay of bulk phage mRNA as determined by hybridization is much slower, with a half-life of 10·6 minutes. The inactivating event for A messages frequently occurs before the RNA polymerase has reached the 3′-end of the gene. The capsid genes F, G and H are contiguous and exhibit polarity, suggesting that the expression of these three genes is regulated in part by a common mRNA functional-decay rate. For the contiguous genes B and C , the similarity of their inactivation rates suggests that they too might show polarity. Amber mutants in B indeed cause at least an 80% reduction in the amount of C protein synthesis. The two gene clusters, B-C and F-G-H , allow recognition of a new type of mRNA unit, characterized by the similar functional stabilities of the component genes. The existence of units of functional stability suggests possible mechanisms for mRNA degradation and the regulation of protein synthesis.