The bacteriophage T4 lysozyme gene is transcribed at early and late times after infection of E. coli, but the early mRNA is not translated. DNA sequence analysis and mapping of the 5′ ends of the lysozyme transcripts produced at different times after T4 infection show that the early mRNA is Initiated some distance upstream from the gene. The early mRNA is not translated because of a stable secondary structure which blocks the translational initiation site. The stable RNA structure has been demonstrated by nudease protection in vivo After DNA replication begins, two late promoters are activated; the late transcripts are initiated at sites such that the secondary structure can not form, and translation of the late messages occurs.
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