Mechanism of transcription in the N operon of bacteriophage lambda

Termination of transcription by nusA gene protein of Escherichia coli

The nusA gene protein of Escherichia coli and N gene protein of bacteriophage lambda interact in vitro and cooperate in vivo to prevent transcription termination. In vitro the nusA gene protein causes RNA polymerase to pause in the tR2 terminator region of lambda DNA. A completed termination event at tR2 requires both the nusA gene protein and the previously described E. coli termination factor rho. The nusA gene protein is therefore both a transcription termination factor and a protein which couples antitermination factors to the elongating transcription complex.

Isolation and genetic characterization of the nitA mutants of Escherichia coli affecting the termination factor rho

Taking advantage of the Spi (sensitivity to P2 interference) phenomenon, bacterial mutants seemingly resistant to phage lambdasusNnin5, but sensitive to phage lambdaspi, were isolated from a strain of E. coli K12 carrying no nonsense suppressor and lysogenic for P2. A class of these mutants, designated nitA (N-independent transcription), is described here. Upon infection of the nitA mutants with a trp transducing phage lambdasusN7N53ptrp46 which carries the E. coli trpE and D genes in the CIII-att region of the lambda genome, formation of anthranilate synthetase (ASase, a complex protein of trp E and D gene products) was clearly demonstrated. In contrast, no ASase formation was observed in the parent nitA+ strain under the same conditions. The synthesis is subject to "turn off" control, and is completely repressed by the CI repressor of phage lambda. The nitA cells lysogenic for lambdaCI857susN7N53 are killed by thermal induction much more efficiently than the parent cells lysogenic for the same phage. The nitA mutants support the growth of lambdasusN7N53byp much better than the parent. These results suggest that the nitA mutation permits the early leftward and rightward transcription of the lambda genome in the absence of the N gene product. On the E. coli genetic map, nitA is located between ilv and metE, nearer to ilv. The mutant allele is recessive to the wild-type allele. The present evidence, together with results of biochemical investigations to be reported, suggests that nitA is a gene specifying the transcription termination factor rho.

Synthesis and degradation of early mRNA in lambda phage

Using two different Escherichia coli mutants defective in elongation factors EFG and EFTs required for peptide synthesis, lambda phage with or without a tof mutation was analysed for synthesis of early mRNA by DNA-RNA hybridization technique. (1) In CP78G carrying temperature-sensitive elongation factor G, shift-up to high temperature (41 degrees C) in the middle of phage infection did not affect early mRNA synthesis with lambdatof+ phage but did inhibit it with lambdatof- phage. (2) In HAK88 carrying temperature-sensitive elongation factor Ts, shift-up to 41 degrees C dropped total cellular RNA synthesis to below 10-20 percent of the control in the presence or absence of phage infection (stringent control). Under such a condition for suppressed protein synthesis, lambda early mRNA synthesis was completely blocked with both tof+ and tof- phage infection. Thus, stringent control seems to exert its effect on lambda early mRNA synthesis. (3) Addition of chloramphenicol, which is known to relax the stringent control of RNA synthesis, to the culture of phage-infected HAK88 at 41 degrees C resulted in full recovery of tof+-mRNA synthesis, but only in partial recovery to tof --mRNA synthesis. (4) Analysis of the stability of lambda mRNA indicated an exponential decay, and a halflife of tof --mRNA of 6 min when that of tof+-mRNA was 13 min at 37 degrees C.

Transcription termination and late control in phage lambda

A transcription termination site occurs between the promoter for late gene expression of bacteriophage lambda and the late genes themselves. It is proposed that the lambda Q gene product controls late gene expression by over-coming this termination barrier.

Bacterial mutants able to partly suppress the effect of N mutations in bacteriophage λ

A method is described whereby bacterial mutants (sun) may be selected which are able to specifically suppress mutations in the N gene of bacteriophage lambda. The sun mutations seem to be allelic to suA mutations, which suppress the polarity of nonsense codons, since suA mutants have all of the properties of sun mutants and both are genetically linked to the ilv gene. In the light of these experiments and recent data by others, models originally suggested to explain polarity in bacterial operons, are discussed with regard to their possible relevance to the mechanism of N action.

Regulation by N gene protein of phage lambda of anthranilate synthetase synthesis in vitro

The N protein of bacteriophage lambda is a positive regulator of early lambda gene expression. In a lambdatrp transducing phage, lambdatrp46Nam, the synthesis of trp enzymes in vivo is also dependent on the presence of active N protein. The DNA of this phage has been used in a protein-synthesizing system in vitro to develop a biochemical assay for the activity of the N protein. From the following observations it appears that it is the N protein itself that stimulates trp enzyme synthesis in vitro. An activity that stimulates trp enzyme synthesis can be made in vitro by lambdaN(+) DNA but not by lambdaNam DNA. This activity can also be detected in extracts of induced lambdaN(+) lysogens but not of lambdaNam lysogens. Furthermore, the activity is temperature sensitive in similar extracts of lambdaNts lysogens. No such activity is detectable in extracts of induced lysogens of lambdaimm(21). This phage makes all lambda-coded gene products outside the immunity region, but lacks an N protein activity able to substitute for N(lambda) protein in vivo. Our experiments also show that the action of N protein is inhibited by the cI repressor protein in vivo as it is in vivo.