No abstract

We have made a derivative of bacteriophage lambda that makes no OOP antisense RNA. The mutant phage carries a point mutation that inactivates the OOP promoter, po. The phages lambda + and lambda po- have identical plaque morphologies, one-step growth curves, and frequencies of lysogenization of a sensitive host. OOP RNA synthesis is weakly repressed by the Escherichia coli LexA protein. Consonant with this inducibility of OOP RNA synthesis by ultraviolet light, we find a two-fold greater phage burst following ultraviolet induction of a lambda + than of a lambda po- prophage. In lambda + infections, OOP RNA causes two cleavage events in cll mRNA: one is in the 3'-end of the coding region, and the second is in the intercistronic region between the cll and O genes. The cll gene fragments are subject to additional hydrolytic events, and cll mRNA levels are several-fold lower in lambda + than in lambda po- infections late in the infection cycle. However, O mRNA levels are almost unaffected by the po- mutation.

No abstract

By binding to the DNA site O E at position À60.5 in the gal operon, the GalR protein activates transcription from the P2 promoter located on the opposite face of DNA (position À5) and represses transcription from the P1 promoter located on the same face (position 1). GalR increases RNA polymerase binding at P2 and inhibits isomerization at P1 by forming a GalR-DNA-RNA polymerase ternary complex in each case. The speci®c effect of GalR at one promoter is independent of the presence of the other promoter. The enhancement or repression is also not the intrinsic property of a promoter; the regulation can be reversed by switching the angular orientation of the promoters relative to O E . Both enhancement and repression appear to require the same interaction between RNA polymerase a-subunit and GalR and/or the same interaction between RNA polymerase a-subunit and DNA in the ternary complexes. We have discussed how GalR might exert opposite effects in the steps involved in the formation of the open complex from free RNA polymerase and DNA.