mRNA stabilizing signals encoded in the genome of the bacteriophage phi x174.

In Escherichia coli cells infected with bacteriophage ϕx174, mRNAs initiated by promoters PB and PD terminate after genes J, F, G, or H (TJ, TF, TG, or TH). These RNAs are relatively stable and contain mRNA-stabilizing signals at their 3′ ends. These signals were cloned after gene D of ϕx174 in an expression vector plasmid. The cloned signals stabilize mRNA of the upstream gene D and the stabilized mRNA is translationally functional. When these signals are inserted in reverse, no stabilizing effect on mRNA is observed indicating that the correct sequences at the 3′ ends of transcripts determine their stability. When a stabilizing signal (+) and a mutated stabilizing signal (-) which has reduced stabilizing activity are tandemly inserted after gene D, two sets of 3′ termini of the transcript are observed indicating that both signals also function as terminators. The amount of gpD synthesized from these constructs varies depending upon the relative positions of the (+) or (-) signals after gene D. The stabilizing function seems to act by preventing mRNA degradation from the 3′ to 5′ direction. Several common features of these stabilizers are described.