In vitro regulation of phage lambda cII gene expression by Escherichia coli integration host factor.

Abstract

The effect of Escherichia coli integration host factor (IHF) on phage A gene expression has been examined in a simplified DNA-directed in vitro system that measures the formation of the first dipeptide of the gene product. Plasmid pKC3OcII, which contains the phage A genes N, ciH and 0, under control of the PL promoter, was used as template to study the expression of the first dipeptide of the gene products-i.e., fMet-Asp for N protein, fMet-Val for cII, and fMet-Thr for 0. Purified IHF stimulates the DNA-directed synthesis of fMet-Val (cdi) and fMet-Thr (0) 2-3-fold but has no effect on the synthesis of fMet-Asp (N). In this in vitro system, the stimulation by IHF of cII and 0 gene expression is at the level of transcription. Phage A repressor completely inhibits dipeptide synthesis in the presence or absence of IHF. The results are consistent with a role of IHF as a transcription antiterminator, perhaps functioning at or near the tRl site preceding the cII gene.

Translation initiation of bacteriophage lambda gene cII requires integration host factor

“…1). Consistent with this idea is the demonstration that cII synthesis in a coupled transcription-translation system is IHF dependent (this work and reference 23).…”

“…IHF augmented the synthesis of cII mRNA; addition of IHF to clI mRNA did not increase clI translation. These authors concluded that IHF stimulates cII transcription by suppressing termination at tRl, which lies just promoter-proximal to cII (23).…”

“…Such structures are known to block translation initiation (10,25,27 In contrast to the in vivo studies described above, analysis of cII expression in a purified in vitro system suggests a role for IHF in cII transcription. Peacock et al (23) found that in vitro, IHF stimulated coordinately both the synthesis of cII protein (or initial cII dipeptide) and that of a downstream gene product; expression of the upstream N gene was IHF independent. IHF augmented the synthesis of cII mRNA; addition of IHF to clI mRNA did not increase clI translation.…”

“…In the presence of IHF, cII mRNA is released in a translatable configuration, whereas in the absence of host factor, the released transcript carries a blocked ribosome binding site. This model can be accommodated to the observations of Peacock et al (23) by assuming that in vitro tRl can act as a terminator rather than as a pause site. Transcription through tRl might be modulated by factors absent or limiting in the in vitro system.…”

Integration host factor is required for the activation of developmentally regulated genes in Caulobacter.

“…IHF-binding sites have been identified in several bacterial (r 7~ promoter regions. These include the E. coli ilvG-MEDA operon, some bacteriophage Mu promoters, and the ~ PL and pcin promoters (Pereira et al 1988;van Rijn et al 1988;Peacock et al 1984;Griffo et al 1989). In the case of the ilvGMEDA operon, IHF binding exerts a repressive effect on the transcription of the ilvGpl pro-…”