Activation and quantitative estimation of bacteriophage T4 late regulatory signal in cis- and transconditions

Activation of the bacteriophage T4 late gene 22 carried on the phage genome (ciscondition) or borne on a plasmid (transcondition) was quantitatively analyzed after phage infection using a lacZ reporter gene. Transcription from the late promoter was activated postreplicatively by concomitantly infecting T4 phage. A truncated T4-lacZ gene including only 15 bp of sequence upstream of the late promoter consensus of gene 22 TATAAATA, was fully activated in the ciscondition but induced to a reduced extent in the transcondition. A possible mechanism for trans-activation is discussed.