Specificity of polarity suppression in E. coli: correction of defects in gene N, but not in gene Q, of phage lambda

The Psu protein of bacteriophage P4 is an antitermination factor for rho-dependent transcription termination

A 0.7-kbp DNA fragment from bacteriophage P4 that contained the polarity suppression (psu) gene was cloned in an expression plasmid. Induction of the plasmid-borne psu gene resulted in the overproduction of a protein having the biological properties of the P4-induced polarity suppressor. In vivo, Psu protein acted in trans to suppress rho-dependent polarity in the late genes of an infecting P2 phage, in plasmid operons, and in the host chromosome. Psu action did not require the presence of other P2 or P4 phage genes. Psu caused efficient readthrough (antitermination) by Escherichia coli RNA polymerase at the rho-dependent terminators tR1 and TIS2, individually and in tandem, but did not affect termination at rho-independent sites. Neither the conserved antitermination sequence boxA nor any unique promoter or utilization sequence was required for Psu activity.

Transcription and membrane attachment of bacteriophage lambda DNA in the absence of N function in the E. coli suA 1 mutant

In the polarity suppressor strain psuA 1, we observe a partial N independence of both transcription and DNA-membrane attachment for a lambda NN mutant. These results, in agreement with the genetical data reported by Dambly et al. (1976), suggest that the N product and rho factor are involved in the same process but may not interact directly.

Transposable genetic elements as agents of gene instability and chromosomal rearrangements

Transposable genetic elements in prokaryotes and eukaryotes, when inserted at a given locus, can control expression of the locus and cause large scale rearrangements of adjacent DNA sequences. Striking similarities in genetic behaviour between the two groups of elements have led to the proposal of a molecular model of eukaryotic controlling elements, and to suggestions about the part such elements may play in evolution and differentiation.

Bacteria with defective rho factors suppress the effects of N mutations in bacteriophage lambda

A prediction based on the model for N-gene function of bacteriophage lambda proposed by Roberts (1971) is confirmed by showing that a lambdaN- double mutant is able to grow in strains of E. coli with defective rho transcription termination factors. The burst sizes for lambdaN- in these strains range from 5 to 24% the burst sizes for lambdaN+ in the same strain. This low level of suppression is also evident in the levels of synthesis of the lambda exonuclease and is consistent with other evidence that the defect in the rho factors of these strains is only partial. These strains do not suppress the effects of mutations in genes O, P and Q of lambda nor in genes 30 and 43 of bacteriophage T4. The lack of suppression of lambdaQ- is significant because the Q-gene product, like the N-gene product, is believed to function as an anti-terminator of lambda transcription but at termination sites that may not require rho factor action.

Efficient suppression of the requirement for N function of bacteriophage lambda by a Rho-defective E.coli suA mutant

The E. coli suA mutant (T82), which is a suppressor of polarity by virtue of its impaired transcription termination factor (rho) activity, is shown to be an efficient suppressor of lambdaN- mutants. The relief of the N requirement by this host is reflected in a substantial restoration of growth and N-dependent beta-galactosidase expression as well as in a partial relief of polarity of N-defective phages.