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PubMed2003

Adenovirus type 5 DNA binding protein stimulates binding of DNA polymerase to the replication origin.

The adenovirus (Ad) DNA-binding protein (DBP) is essential for the elongation phase of Ad DNA replication by unwinding the template in an ATP-independent fashion, employing its capacity to form multimers. DBP also enhances the rate of initiation, with the highest levels obtained at low concentrations of Ad DNA polymerase (Pol). Here, we show that stimulation of initiation depends on the template conformation. Maximal stimulation, up to 15-fold, is observed on double-stranded or viral TP-containing origins. The stimulation is reduced on partially single-stranded origins and DBP does not enhance initiation any more once the origin is completely unwound. This suggests a role for DBP in origin unwinding that is comparable to its unwinding capacity during elongation. However, mutant DBP proteins defective in unwinding and elongation can still enhance initiation on ds templates. DBP also stimulates the binding of nuclear factor I (NFI) to the origin and lowers the K(m) for coupling of the first nucleotide to the precursor terminal protein by Pol. Mobility shift experiments reveal that DBP stimulates the binding of Pol on double-stranded origin and nonorigin DNA but not on single-stranded DNA. This effect is specific for DBP and is also seen with other DNA Pols. Our results suggest that, rather than by origin unwinding, DBP enhances initiation by modulating the origin conformation such that DNA Pol can bind more efficiently.

Adenoviridae↗
PubMed1995

Reduction of chromium(VI) by ascorbate leads to chromium-DNA binding and DNA strand breaks in vitro.

Chromium(VI) is a known human carcinogen which requires intracellular reduction for activation. Ascorbate (vitamin C) has been reported to function as a major reductant of Cr(VI) in animals and cell culture systems. The reaction of Cr(VI) with varying concentrations of ascorbate was studied under physiological conditions in vitro in order to determine the types of reactive intermediates produced and to evaluate the reactivity of these intermediates with DNA. Reactions of 1.8 mM Cr(VI) with 0-18 mM ascorbate at pH 7.0 in N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES; 0.10 M) and tris(hydroxymethyl)aminomethane hydrochloride (Tris.HCl; 0.050 M) buffers were studied by electron paramagnetic resonance and UV/visible spectroscopy. Cr(V) and carbon-based free radical adducts of 5,5-dimethyl-1-pyrroline 1-oxide (DMPO) were observed at 0.5 to 1 and 1 to 1 reactions of ascorbate to Cr(VI). Levels of Cr(V) were higher for reactions in HEPES buffer, and levels of carbon-based radicals were higher in Tris.HCl buffer. Levels of Cr(IV) and Cr(III) increased with increasing concentration of ascorbate in both buffers. Reaction of Cr(VI) with varying ascorbate in the presence of calf thymus DNA or pBR322 DNA resulted in Cr-DNA adducts and plasmid relaxation, respectively. Maximum binding of Cr to DNA was observed for the 1:1 reaction ratio of Cr(VI) with ascorbate in both HEPES and Tris.HCl buffers, but total Cr bound to DNA was 8-fold lower in Tris.HCl than HEPES buffer. Preincubation of Cr(VI) with ascorbate before reaction with DNA decreased Cr-DNA binding to background levels. Preincubation of Cr(III) with ascorbate resulted in only low Cr-DNA binding. Levels of Cr-DNA binding were higher with single-stranded vs double-stranded DNA. Reactions with 14C-labeled ascorbate produced no cross-linking of ascorbate to DNA. Maximum plasmid relaxation was observed for the 1:1 ascorbate to Cr(VI) ratio in both buffers; however, single-strand breaks were 2-fold higher in Tris.HCl than HEPES buffer. Reactions with plasmid in the presence of DMPO quenched formation of single-strand breaks. Interpretation of these results in light of the spectroscopic studies suggested that Cr(V) and carbon-based radicals were responsible for Cr-DNA adducts and DNA single-strand breaks, respectively.

Ascorbic Acid↗
PubMed1999

PBX and MEIS as non-DNA-binding partners in trimeric complexes with HOX proteins.

HOX, PBX, and MEIS transcription factors bind DNA through a homeodomain. PBX proteins bind DNA cooperatively as heterodimers with MEIS family members and also with HOX proteins from paralog groups 1 to 10. MEIS proteins cooperatively bind DNA with ABD-B class HOX proteins of groups 9 and 10. Here, we examine aspects of dimeric and higher-order interactions between these three homeodomain classes. The most significant results can be summarized as follows. (i) Most of PBX N terminal to the homeodomain is required for efficient cooperative binding with HOXD4 and HOXD9. (ii) MEIS and PBX proteins form higher-order complexes on a heterodimeric binding site. (iii) Although MEIS does not cooperatively bind DNA with ANTP class HOX proteins, it does form a trimer as a non-DNA-binding partner with DNA-bound PBX-HOXD4. (iv) The N terminus of HOXD4 negatively regulates trimer formation. (v) MEIS forms a similar trimer with DNA-bound PBX-HOXD9. (vi) A related trimer (where MEIS is a non-DNA-binding partner) is formed on a transcriptional promoter within the cell. (vii) We observe an additional trimer class involving non-DNA-bound PBX and DNA-bound MEIS-HOXD9 or MEIS-HOXD10 heterodimers that is enhanced by mutation of the PBX homeodomain. (viii) In this latter trimer, PBX is likely to contact both MEIS and HOXD9/D10. (ix) The stability of DNA binding by all trimers is enhanced relative to the heterodimers. These findings suggest novel functions for PBX and MEIS in modulating the function of DNA-bound MEIS-HOX and PBX-HOX heterodimers, respectively.

Antennapedia Homeodomain Protein↗
PubMed1992

DNA-binding and non-DNA-binding forms of the transformed glucocorticoid receptor.

In this work we have probed the mechanism responsible for two non-DNA-binding states of the mouse glucocorticoid receptor. In the first case, transformed receptors were treated with hydrogen peroxide. It is known that oxidizing agents promote the formation of disulfide bonds in the glucocorticoid receptor, but it has not been determined what domains are involved in any disulfide bond formation that leads to inactivation of DNA-binding activity. We show here that hydrogen peroxide inhibits DNA-binding by the 15-kDa tryptic fragment containing the DNA-binding fingers with the same concentration dependency as it inhibits DNA-binding by the uncleaved receptor. This suggests that all of the effect of peroxide is on sulfhydryl groups within the zinc fingers. After dissociation (transformation) of cytosolic heteromeric glucocorticoid receptor complexes, only a portion (40-60%) of the dissociated receptors can bind to DNA-cellulose. We show that the 15-kDa tryptic fragment derived from the portion of transformed receptors that do not bind to DNA is itself competent at DNA-binding.

Animals↗
PubMed2000

Functional mapping of the MH1 DNA-binding domain of DPC4/SMAD4.

The transcription factor Smad4 binds DNA in response to a TGF-beta ligand-initiated intracellular signaling cascade. SMAD4 is deleted or mutated during tumorigenesis in many human tumors. Some of these mutations occur in the N-terminal portion of the protein, the Mad homology 1 (MH1) region, which exhibits sequence-specific DNA-binding. We used alanine scanning mutagenesis and natural mutations to map the subregion of the MH1 domain necessary for that function. We created 20 individual mutations in the MH1 region of human Smad4 and assayed their effect on DNA-binding in vitro. Mutation of residues in the less conserved N- and C-terminal areas of the MH1 region had no effect on DNA-binding. However, mutations in the domain from L43 to R135 caused a dramatic reduction of the ability of Smad4 to bind DNA. Previous work demonstrated a beta-hairpin protein motif within this region to be responsible for DNA-binding, but suggested that the tumorigenic mutations occurring outside this motif may target a separate function of the MH1 domain. Our results demonstrate that the MH1 domain as a whole is very sensitive to changes in overall structure, and that tumorigenic mutations within the region of L43-R135 indeed would target DNA-binding.

Amino Acid Sequence↗
PubMed1999

Reduction of G-box binding factor DNA binding activity, but not G-box binding factor abundance, causes the downregulation of RBCS2 expression during early tomato fruit development.

The downregulation of RBCS2 promoter activity during tomato fruit development has been investigated by transient gene expression. A major drop in promoter activity occurs between 5 and 25 mm fruit diameter, corresponding to the late cell division to early cell enlargement phase. This drop is abolished by a mutation of the single G-box element necessary for high RBCS2 promoter activity in young tomato fruit. The G-box binding activity of fruit nuclear and total protein extracts drops concomitantly with the reduction of RBCS2 promoter activity while G-box binding factor expression is not affected. The data indicate that the developmental signal that downregulates the RBCS2 promoter acts on the regulation of DNA binding activity of constitutively expressed G-box binding factors.

Arabidopsis↗
PubMed2002

Green fluorescent protein modified to bind DNA initiates production of anti-DNA antibodies when expressed in vivo.

Studies have clearly demonstrated that DNA itself is not or scarcely immunogenic in experimental animals. We have previously demonstrated that linking human polyomavirus large T-antigen to DNA rendered DNA immunogenic irrespective of the source or the structure of DNA. As an alternative to this artificial system, in vivo expression of the DNA binding protein large T-antigen of human polyomaviruses also resulted in the production of anti-DNA antibodies. This observation demonstrates that the large T-antigen concept is operational in vivo and supports the idea that complex formation between a non-self DNA-binding protein and DNA renders DNA immunogenic in analogy to a hapten-carrier model. To further investigate this model, the DNA binding domain (DBD) of a self-protein (glucocorticoid receptor) was linked to a non-DNA binding non-self protein, the green fluorescent protein (GFP). Immunization of mice with an expression plasmid for this fusion protein resulted in the production of anti-DNA antibodies, while mice inoculated with either a plasmid encoding the GFP or a plasmid encoding the DBD of the glucocorticoid receptor failed to produce anti-DNA antibodies. These results demonstrate that DNA may become immunogenic through in vivo association with any non-self DNA binding protein. Considering these data in context of results obtained with the polyomavirus large T-antigen, one may conclude that viral DNA-binding proteins may affect the regulation of immune tolerance to DNA and nucleosomes in vivo.

Amino Acid Sequence↗
PubMed2001

Kinetic studies of Fos.Jun.DNA complex formation: DNA binding prior to dimerization.

The bZIP proteins Fos and Jun bind DNA rapidly and with high affinity, forming a heteromeric complex that mediates activated transcription. Here we use stopped-flow fluorescence resonance energy transfer (FRET) to study the kinetic pathway by which Fos.Jun. DNA complexes assemble. Though dimerization of Fos and Jun occurs rapidly in the absence of DNA, the rate of dimerization is enhanced in the presence of DNA. Global analysis of the kinetic data shows that the favored DNA binding pathway is one is which the two protein monomers bind DNA sequentially and assemble their dimerization interface while bound to DNA.

Amino Acid Sequence↗
PubMed2000

MIDA1 is a sequence specific DNA binding protein with novel DNA binding properties.

BACKGROUND: Id proteins not only regulate cell differentiation negatively, but they also promote growth and apoptosis. To know the mechanism of how Id regulates cell fate, we previously isolated an Id-associating protein, MIDA1, which positively regulates cell growth. Its predicted amino acid sequence contains tryptophan-mediated repeats (Tryp-med repeats) similar to the DNA binding region of the c-Myb oncoprotein. We determined whether MIDA1 can bind to DNA in a sequence specific manner by PCR-assisted binding site selection. RESULTS: We identified a 7-base sequence (GTCAAGC) surrounded by a 1-3 bp palindromic sequence as the DNA sequence recognized by the Tryp-med repeats of MIDA1. This motif is located within the 5'-flanking sequence of several growth regulating genes. Gel shift assays revealed that this sequence and a certain length of flanking DNA are necessary for MIDA1 to bind DNA in a stable manner. Methylation interference and DNase I footprint analysis suggested that the DNA binding of MIDA1 is resistant to DNA methylation and that MIDA1 does not specifically localize on this particular motif. CONCLUSIONS: We concluded that MIDA1 is a novel sequence-specific DNA binding protein with some different properties from the usual transcription factors and that MIDA1 may act as a mediator of Id-mediated growth-promoting function through its DNA binding activity.

Base Sequence↗
PubMed1994

Escherichia coli single-stranded DNA-binding protein: multiple DNA-binding modes and cooperativities.

There are now several well-documented SSBs from both prokaryotes and eukaryotes that function in replication, recombination, and repair; however, no "consensus" view of their interactions with ssDNA has emerged. Although these proteins all bind preferentially and with high affinity to ssDNA, their modes of binding to ssDNA in vitro, including whether they bind with cooperativity, often differ dramatically. This point is most clear upon comparing the properties of the phage T4 gene 32 protein and the E. coli SSB protein. Depending on the solution conditions, Eco SSB can bind ssDNA in several different modes, which display quite different properties, including cooperativity. The wide range of interactions with ssDNA observed for Eco SSB is due principally to its tetrameric structure and the fact that each SSB protomer (subunit) can bind ssDNA. This reflects a major difference between Eco SSB and the T4 gene 32 protein, which binds DNA as a monomer and displays "unlimited" positive cooperativity in its binding to ssDNA. The Eco SSB tetramer can bind ssDNA with at least two different types of nearest-neighbor positive cooperativity ("limited" and "unlimited"), as well as negative cooperativity among the subunits within an individual tetramer. In fact, this latter property, which is dependent upon salt concentration and nucleotide base composition, is a major factor influencing whether ssDNA interacts with all four or only two SSB subunits, which in turn determines the type of intertetramer positive cooperativity. Hence, it is clear that the interactions of Eco SSB with ssDNA are quite different from those of T4 gene 32 protein, and the idea that all SSBs bind to ssDNA as does the T4 gene 32 protein must be amended. Although it is not yet known which of the Eco SSB-binding modes is functionally important in vivo, it is possible that some of the modes are used preferentially in different DNA metabolic processes. In any event, the vastly different properties of the Eco SSB-binding modes must be considered in studies of DNA replication, recombination, and repair in vitro. Since eukaryotic mitochondrial SSBs as well as SSBs encoded by prokaryotic conjugative plasmids are highly similar to Eco SSB, these proteins are likely to show similar complexities. However, based on their heterotrimeric subunit composition, the eukaryotic nuclear SSBs (RP-A proteins) are significantly different from either Eco SSB or T4 gene 32 proteins. Further subclassification of these proteins must await more detailed biochemical and biophysical studies.

Allosteric Regulation↗
PubMed1999

Zinc finger of replication protein A, a non-DNA binding element, regulates its DNA binding activity through redox.

Eukaryotic replication protein A (RPA) is a single-stranded DNA-binding protein with multiple functions in DNA replication, repair, and genetic recombination. RPA contains an evolutionarily conserved 4-cysteine-type zinc finger motif (X(3)CX(2-4)CX(12-15)CX(2)C) that has a potential role in regulation of DNA replication and repair (Dong, J., Park, J-S., and Lee, S-H. (1999) Biochem. J. 337, 311-317 and Lin, Y.-L., Shivji, M. K. K., Chen, C., Kolodner, R., Wood, R. D., and Dutta, A. (1998) J. Biol. Chem. 273, 1453-1461), even though the zinc finger itself is not essential for its DNA binding activity (Kim, D. K., Stigger, E., and Lee, S.-H. (1996) J. Biol. Chem. 271, 15124-15129). Here, we show that RPA single-stranded DNA (ssDNA) binding activity is regulated by reduction-oxidation (redox) through its zinc finger domain. RPA-ssDNA interaction was stimulated 10-fold by the reducing agent, dithiothreitol (DTT), whereas treatment of RPA with oxidizing agent, diazene dicarboxylic acid bis[N,N-dimethylamide] (diamide), significantly reduced this interaction. The effect of diamide was reversed by the addition of excess DTT, suggesting that RPA ssDNA binding activity is regulated by redox. Redox regulation of RPA-ssDNA interaction was more effective in the presence of 0.2 M NaCl or higher. Cellular redox factor, thioredoxin, was able to replace DTT in stimulation of RPA DNA binding activity, suggesting that redox protein may be involved in RPA modulation in vivo. In contrast to wild-type RPA, zinc finger mutant (cysteine to alanine mutation at amino acid 486) did not require DTT for its ssDNA binding activity and is not affected by redox. Together, these results suggest a novel function for a putative zinc finger in the regulation of RPA DNA binding activity through cellular redox.

Amino Acid Sequence↗
PubMed2025

Moss BRCA2 lacking the canonical DNA-binding domain promotes homologous recombination and binds to DNA.

BRCA2 is crucial for mediating homology-directed DNA repair (HDR) through its binding to single-stranded DNA (ssDNA) and the recombinases RAD51 and DMC1. Most BRCA2 orthologs have a canonical DNA-binding domain (DBD) with the exception of Drosophila melanogaster. It remains unclear whether such a noncanonical BRCA2 variant without DBD possesses a DNA-binding activity. Here, we identify a new noncanonical BRCA2 in the model plant Physcomitrium patens (PpBRCA2). We establish that PpBRCA2 is essential for genome integrity maintenance, somatic DNA double-strand break (DSB) repair, HDR-mediated gene targeting, and RAD51 foci recruitment at DNA break sites. PpBRCA2 is also critical for DSB repair during meiosis. Interestingly, PpBRCA2 interacts strongly with RAD51 but weakly with DMC1, suggesting a distinct meiotic function compared to other BRCA2 homologs. Despite lacking the canonical DBD, PpBRCA2 binds ssDNA through its disordered N-terminal region and efficiently promotes HDR. Our work highlights that the ssDNA binding capacity of BRCA2 homologs is conserved regardless of the presence of a canonical DBD and provides a deeper understanding of BRCA2's functional diversity across species.

BRCA2 Protein↗
PubMed1988

DNA-binding studies with 6BT and 5I: implications for DNA-binding/carcinogenicity and DNA-binding/mutagenicity correlations.

The divergent activities of a reported carcinogen/noncarcinogen pair of monoazo dyes related to the hepatocarcinogen Butter Yellow (DAB) are currently under investigation in our laboratories. As part of these studies we have determined (a) target organ distribution after oral dosing to rats and (b) covalent binding of 14C-labelled compound to DNA. In DNA-binding studies, 3 rat liver-metabolising systems were employed: in vivo (whole liver), isolated intact hepatocytes, and liver subcellular fractions. Distribution studies revealed that comparable levels of both compounds were detected in the liver at similar times after dosing, and these in vivo tissue concentrations were used for in vitro DNA-binding studies. At this 'in vivo equivalent dose', the carcinogen was consistently bound to DNA more effectively, and the difference (ratio of DNA binding) between the 2 compounds was far greater in vivo. In subsequent studies, covalent DNA binding to bacterial (Salmonella) DNA was assessed at the in vivo equivalent dose. In contrast to the afore-mentioned findings in mammalian systems, the carcinogen was bound less effectively to DNA, and gave fewer revertant counts/plate when the 2 compounds were bound to an equivalent extent. These data are discussed in view of their implications for DNA-binding/carcinogenicity correlations, and with respect to the relationship between DNA binding and mutagenicity in the Salmonella assay.

Animals↗
PubMed1979

Messenger RNA for the Ad2 DNA binding protein: DNA sequences encoding the first leader and heterogenity at the mRNA 5' end.

During the early stage of Ad2 infection of human cells, RNA is transcribed from five separate transcription units. Early region II encodes the mRNA for a 72K single-stranded DNA binding protein (DBP) which functions in DNA replication. This report describes the structure of the first leader of the DBP mRNA and the flanking sequences in the DNA. The leader, labeled in vivo with 32P, was isolated by DNA filter hybridization to the viral restriction fragment Eco RI F, and its RNAase T1 and RNAase A oligonucleotides were analyzed by RNA fingerprinting techniques. Comparison of this RNA sequence information with the DNA sequence of Eco RI F has located a 68 nucleotide region of the Hae III C subfragment at coordinate 75.1 that encodes the leader. This position is near the coordinate to which nascent chain analysis and ultraviolet transcription mapping have mapped an RNA initiation site, or promoter, for the DBP mRNA. The DNA sequence that overlaps the leader on the 3' side contains a donor sequence for splicing this leader to a second downstream leader. The splicing sequence shows a seven base homology with the comparable structure of the Ad2 major late leader, and a mouse globin mRNA splicing sequence. The DNA sequence upstream from the cap, the region oof the potential promoter site does not, however, contain a "TA-TAAA"-type homology of the sort noted by D. Hogness, M. Goldberg and R. Lifton (personal communication) for many cellular transcription units, and by other investigations for the Ad2 major late transcription unit. Also, the leader is found with two distinct capped 5' termini, 7meGpppA and 7meGpppG, which are encoded at adjacent positions in the DNA and thus are from mRNAs which are staggered by one nucleotide in length at the 5' end. The staggering at the 5' terminus and the lack of the upstream homolgy distinguish the DBP mRNA from many viral and cellular messenger. In both these respects, however, the DBP mRNA resembles the late messengers of SV40 and polyoma viruses. In this paper, we discuss the implications of these findings for the mechanism of specifying mRNA 5' ends.

Adenoviruses, Human↗
PubMed1999

Mutational analysis of the PapB transcriptional regulator in Escherichia coli. Regions important for DNA binding and oligomerization.

PapB is a transcriptional regulator in the control of pap operon expression in Escherichia coli. There are PapB homologous proteins encoded by many fimbrial gene systems that are involved in the regulation of fimbriae-adhesin production, and previous studies suggested that PapB binds DNA through minor groove contact. Both deletion and alanine-scanning mutagenesis were used to identify functionally important regions of the PapB protein. Mutations altering Arg61 or Cys65 caused deficiency in DNA binding, indicating that these residues are critical for PapB binding to DNA. Alanine substitutions at positions 35-36, 53-56, and 74-76 resulted in mutants that were impaired in oligomerization. All these amino acid residues are conserved among the PapB homologous proteins, suggesting their importance in the whole family of regulatory proteins. The transcriptional efficiency of all the mutants was clearly reduced as compared with that of wild-type PapB. Taken together, we have localized regions in the PapB protein that are involved in DNA binding and oligomerization, and our results show that both functions are required for its activity as a transcriptional regulator.

Amino Acid Sequence↗
PubMed2001

The wing in yeast heat shock transcription factor (HSF) DNA-binding domain is required for full activity.

The yeast heat shock transcription factor (HSF) belongs to the winged helix family of proteins. HSF binds DNA as a trimer, and additional trimers can bind DNA co-operatively. Unlike other winged helix-turn-helix proteins, HSF's wing does not appear to contact DNA, as based on a previously solved crystal structure. Instead, the structure implies that the wing is involved in protein-protein interactions, possibly within a trimer or between adjacent trimers. To understand the function of the wing in the HSF DNA-binding domain, a Saccharomyces cerevisiae strain was created that expresses a wingless HSF protein. This strain grows normally at 30 degrees C, but shows a decrease in reporter gene expression during constitutive and heat-shocked conditions. Removal of the wing does not affect the stability or trimeric nature of a protein fragment containing the DNA-binding and trimerization domains. Removal of the wing does result in a decrease in DNA-binding affinity. This defect was mainly observed in the ability to form the first trimer-bound complex, as the formation of larger complexes is unaffected by the deletion. Our results suggest that the wing is not involved in the highly co-operative nature of HSF binding, but may be important in stabilizing the first trimer bound to DNA.

Amino Acid Motifs↗
PubMed1993

A cellular factor stimulates the DNA-binding activity of MyoD and E47.

We show that mixing purified MyoD and E47 proteins results in heterodimers that fail to bind DNA, even though MyoD and E47 homodimers can bind DNA efficiently. Addition of cell extracts or a specific fraction from a cell extract enables the heterodimer to bind DNA, but components in this fraction fail to enter the DNA complex. The activity is sensitive to heat and protease and is not ATP-dependent. The activity functions on E47 and MyoD homodimers and can stimulate DNA binding of the basic-helix-loop-helix region of MyoD. The effectiveness of the activity, for MyoD homodimers, depends on the exact DNA sequence of the binding site. Our results suggest that specific factors in the cell might control the DNA-binding properties of helix-loop-helix proteins.

Base Sequence↗
PubMed1993

Human p53 binds DNA as a protein homodimer but monomeric variants retain full transcription transactivation activity.

Wild-type human p53 protein is able to self-associate and consists predominantly of homotetramers in solution. In earlier work we identified the protein sequence motifs involved in p53 quaternary structure and showed that while monomeric p53 protein retains tumour suppressor function, monomeric tumour mutant p53 lacks dominant transforming activity. In this report we use point mutated and truncated cDNA genes encoding self-association defective human p53 proteins to investigate the relationship between p53 protein quaternary structure and the associated activities of transcription transactivation and target specific DNA binding. We show that p53 binds to a target oligonucleotide as a protein homodimer and that p53 dimerisation is required for detectable DNA binding. We found no evidence for p53 tetramer: DNA complexes and we suggest that the quaternary structure status of p53 may regulate a DNA binding associated activity. Monomeric p53 proteins failed to bind DNA in these assays but exhibited increased transactivating activity. Thus, both transcription transactivation and tumour suppressor functions act independently of p53 protein self-association and DNA binding. We propose that our results validate the p53 dimerisation motif as a target for rational anticancer drug design. We predict that compounds able to block p53 dimer assembly would inhibit the dominant transforming activities of mutant p53 in tumours retaining expression of a mutant allele, while leaving intact the wild-type p53 associated activities of transcription transactivation and transformation suppression in unaffected tissue.

Base Sequence↗