Function of the tof gene product in modifying chemical stability of trp messenger RNA synthesized from the PL promoter of lambda trp phage.

The trp operon translocated into the early region of phage lambda can be transcribed under the control of two promoters, the authentic trp promoter (Ptrptrp mRNA) and the PL promoter of the N gene (PLtrp mRNA) (Imamoto and Tani, 1972; Ihara and Imamoto, 1976a). PLtrp mRNA is stabilized with time after infection: at early times after infection chemical degradation of PLtrp mRNA is two-fold slower than for Ptrptrp mRNA, while at later times the stabilization of PLtrp mRNA is almost total. The stabilization of PLtrp mRNA is markedly reduced when the activity of the tof gene product is low due to a missense mutation of the tof gene. In contrast there is no significant reduction in stabilization when N function is lost by an amber mutation. On the basis of these and other experiments with lambdatrp susN7 tof12 phage, it is inferred that stabilization of the PLtrp mRNA is brought about by a modification of the "decay trigger", at least in part by the protein product of the tof gene.