λ Repressor and cro—components of an efficient molecular switch

Johnson, Alexander D.; Poteete, Anthony R.; Lauer, Gail D.; Sauer, Robert T.; Ackers, Gary K.; Ptashne, Mark

doi:10.1038/294217a0

Cited by 390 publications

(268 citation statements)

References 58 publications

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“…Somewhat later the helix-loop-helix group including El2, E47, myoD, and Id were found to form weak but functionally important heterodimers (Tapscott et al 1988;Murre et al 1989;Benezra et al 1990). These reports followed studies in prokaryotes where dimerization is a common characteristic of DNA-binding proteins (for review, see Johnson et al 1981 and references therein). An obvious advantage of the ability of a transcription factor to form homodimers and/or heterodimers is that it provides an opportunity to diversify the number of regulatory mechanisms that can be associated with a single regulatory DNA-binding site.…”

mentioning

confidence: 94%

HNF-1 alpha and HNF-1 beta (vHNF-1) share dimerization and homeo domains, but not activation domains, and form heterodimers in vitro.

Mendel¹,

Hansen²,

Graves³

et al. 1991

Genes Dev.

294

218

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mentioning

confidence: 94%

HNF-1 alpha and HNF-1 beta (vHNF-1) share dimerization and homeo domains, but not activation domains, and form heterodimers in vitro.

Mendel¹,

Hansen²,

Graves³

et al. 1991

Genes Dev.

294

218

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“…For the results reported here, a value of 0.75 was used. The density of the solvent was measured to be 1.004 g/cm 3 with a Paar DMA 602 density meter at 20°C. (This was corrected to 1.006 and 1.003 g/cm 3 at 1 and 25°C, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…Such cooperative activity is known to be involved in the regulation of many protein functions including enzyme activity (1,2), gene expression (3,4), and oxygen transport (5,6). Much of our understanding of this process has come from studies of mammalian hemoglobins (5,6), for which cooperativity manifests itself as a stepwise increase in oxygen affinity as oxygen binding proceeds.…”

mentioning

confidence: 99%

Ligand Linked Assembly of Scapharca Dimeric Hemoglobin

Royer¹,

Fox²,

Smith³

et al. 1997

Journal of Biological Chemistry

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The assembly of Scapharca dimeric hemoglobin as a function of ligation has been explored by analytical gel chromatography, sedimentation equilibrium, and oxygen binding experiments to test the proposal that its cooperativity is based on quaternary enhancement. This hypothesis predicts that the liganded form would be assembled more tightly into a dimer than the unliganded form and that dissociation would lead to lower oxygen affinity. Our experiments demonstrate that although the dimeric interface is quite tight in this hemoglobin, dissociation can be clearly detected in the liganded states with monomer to dimer association constants in the range of 10 8 M ؊1 for the CO-liganded state and lower association constants measured in the oxygenated state. In contrast, the deoxy dimer shows no detectable dissociation by analytical ultracentrifugation. Thus, the more highly hydrated deoxy interface of this dimer is also the more tightly assembled. Equilibrium oxygen binding experiments reveal an increase in oxygen affinity and decrease in cooperativity as the concentration is lowered (in the M range). These experiments unambiguously refute the hypothesis of quaternary enhancement and indicate that, as in the case of human hemoglobin and other allosteric proteins, quaternary constraint underlies cooperativity in Scapharca dimeric hemoglobin.To perform biological activities efficiently, protein molecules have often evolved mechanisms to couple functionally independent subunits. Such cooperative activity is known to be involved in the regulation of many protein functions including enzyme activity (1, 2), gene expression (3, 4), and oxygen transport (5, 6). Much of our understanding of this process has come from studies of mammalian hemoglobins (5, 6), for which cooperativity manifests itself as a stepwise increase in oxygen affinity as oxygen binding proceeds.A particularly simple system for exploring cooperative protein function is the dimeric hemoglobin found in the blood clam Scapharca inaequivalvis, which binds oxygen with a Hill coefficient of 1.5 and shows no change in oxygen affinity or cooperativity as pH varies from 5.5 to 9.0 (7). Although the tertiary structure of the subunits is similar to those of mammalian hemoglobins, the assembly into a cooperative complex is radically different (8). High resolution crystal structure analysis of Scapharca dimeric hemoglobin (HbI) 1 has shown that ligand binding is coupled with significant tertiary rearrangements but very small quaternary changes in the relative subunit dispositions (9, 10).Intersubunit communication depends upon coupling ligand binding with interactions between subunits. As Wyman (11) recognized nearly 50 years ago, cooperative interaction energy may be present as stabilizing energy between unliganded subunits (quaternary constraint; Ref. 12) or liganded subunits (quaternary enhancement; Ref. 13). These alternate conditions can be distinguished either by measuring the strength of the subunit interface as a function of ligation or by following ligand affinity...

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“…It is the length of this DNA rather than its sequence which is important for proper protein recognition. Studies of another positively regulated promoter, XPRM, suggest protein interactions between RNA polymerase and X repressor are required for induction (9,10). For ara PBAD more direct measurements will be required to ultimately prove whether or not specific contacts occur between the proteins involved.…”

Section: Discussionmentioning

confidence: 99%

“…The proteins may interact directly (9,10), or the effects may be indirect, mediated through changes in the DNA structure over significant distances (11,12 All media, plates, and standard procedures including plasmid ligation, transformation and CsCl gradient plasmid isolation were as described in Schleif & Wensink (14).…”

Section: Introductionmentioning

confidence: 99%

Spacing mutations between theEscherichia coliPBAD RNA polymerase binding site and thearaC(I) induction site

1983

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Mutations in the Escherichia coli promoter PBAD have been constructed which alter the spacing of the adjacent RNA polymerase and araC inducer protein binding sites. While deletion of a single base-pair or small insertions do not detectably affect araC protein binding to DNA and they do not alter the conserved sequence of the RNA polymerase binding site, stimulation of PBAD in vivo is greatly reduced. The experiments suggest that the distance or angle between the two proteins on the DNA is critical for promoter function. INTRODUCTIONTranscription from the Escherichia coli L-arabinose operon promoter,

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λ Repressor and cro—components of an efficient molecular switch

Cited by 390 publications

References 58 publications

HNF-1 alpha and HNF-1 beta (vHNF-1) share dimerization and homeo domains, but not activation domains, and form heterodimers in vitro.

HNF-1 alpha and HNF-1 beta (vHNF-1) share dimerization and homeo domains, but not activation domains, and form heterodimers in vitro.

Ligand Linked Assembly of Scapharca Dimeric Hemoglobin

Spacing mutations between theEscherichia coliPBAD RNA polymerase binding site and thearaC(I) induction site

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