THE 2 P2-OGR-LIKE DOMAINS OF THE DELTA-PROTEIN FROM BACTERIOPHAGE-P4 ARE REQUIRED FOR ACTIVITY

The satellite P4 phage Delta protein positively regulates the late gen es of its helper bacteriophage P2, as well as its own late genes. Delt a is a member of a class of activators associated with P2- or P4-like phages and is the largest member of this family. It resembles a covale ntly joined head-to-tail dimer of the other members of this family of activators. We have analyzed the requirement for both standard domains of Delta through the isolation of amber mutants and the insertion of amber linkers. We show that both domains of Delta are required for DNA binding in vivo and for transcriptional activity. Proper spacing betw een the two domains is important for activity at two of the four P2 pr omoters. Expression of both domains from different plasmids causes act ivation of late gene transcription in vivo of all six late promoters o f P2 and P4. A monomric Delta from another satellite phage, phi R73, c an function efficiently as a covalent dimer but when this Delta is mad e dimeric with the second half of P4 delta, it activates less efficien tly. (C) 1997 Academic Press.