Regulation of a bacteriophage T4 late gene, soc, which maps in an early region.

We have sequenced and analyzed the expression of an early region of the bacteriophage T4 genome that surprisingly contains a late gene, soc. soc is oriented in the same direction as early genes, like the T4 lysozyme gene. Northern hybridization of early and late T4 RNA, using cloned T4 restriction fragments as probes, identified two long early transcripts and a short late transcript, all containing the soc-coding sequence. Thus, soc is transcribed both early and late. It is, however, translated only late. The inhibition of soc translation from the long early transcripts can be explained by formation of a hairpin in the RNA that sequesters the soc ribosome-binding site. The transcript initiated at the late promoter cannot form this hairpin and is, therefore, translated.