A cluster of leftward, rho-dependent t'J terminators in the J gene of coliphage lambda

While searching for the N-unresponsive terminator described by Honigman (Gene 13 (1981) 299-309), a 1680-bp DNA fragment from within gene J of bacteriophage lambda was cloned into plasmid pD12 between promoter p'R and the galK gene. In vitro transcription of this plasmid and S1 mapping assays, together with nucleotide sequencing, demonstrated that this DNA fragment contains a cluster of at least four in rho+ Escherichia coli hosts and only 30% in rho- hosts at at 30 degrees C. At the elevated temperature of 42 degrees C, the rho-dependent termination component of the t'J cluster becomes somewhat leaky, with the readthrough increasing by about twofold. The t'J terminators appear to be less responsive to nutR- and N-mediated antitermination (efficiency of 84-87%) than tL3, which responds to the same antitermination function with an efficiency of 97%. The relationship between the t'J cluster and the same antitermination function with an efficiency of 97%. The relationship between the t'J cluster and the highly N-unresponsive leftward termination signal tJ, which is also located within the J gene region (Gottesman et al., J. Mol. Biol. 140 (1980) 57-75; Honigman, Gene 13 (1981) 299-309), is unknown.