title: Max: functional domains and interaction with c-Myc.
abstract: The product of the c-myc proto-oncogene is a DNA-binding protein, the deregulated expression of which is associated with a variety of malignant neoplasms. The cDNA for the max gene was recently cloned as a result of the ability of its protein product to interact with the c-Myc protein. We studied bacterially produced Max, c-Myc, and a series of truncated c-Myc proteins. Full-length c-Myc alone cannot bind DNA. However, a truncated c-Myc protein comprising the basic, helix-loop-helix, and leucine zipper regions can bind specifically to DNA bearing the sequence GGGCAC(G/A)TGCCC. Max protein, either alone or in a heteromeric complex with full-length c-Myc, binds to the same core sequence. Using a novel combination of chemical and photo-cross-linking analysis, we demonstrate that either Max or a c-Myc/Max heteromeric complex binds to DNA virtually exclusively in a dimeric structure. Using fusion proteins in cultured cells, we establish a number of functional characteristics of Max. First, we show that Max can interact with c-Myc intracellularly in a manner dependent on the integrity of the helix-loop-helix and leucine zipper motifs. Second, a nuclear localization domain that contains the sequence PQSRKKLR is mapped to the carboxy-terminal region of Max. Third, Max lacks a transcriptional activation domain that is functional in Chinese hamster ovary cells when fused to a heterologous DNA-binding domain. These data suggest that Max may serve as a cofactor for c-Myc in transcriptional activation or, by itself, as a transcriptional repressor.
authors.affiliation: Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205.
authors.forename: G J
authors.initials: GJ
authors.lastname: Kato
authors.forename: W M
authors.initials: WM
authors.lastname: Lee
authors.forename: L L
authors.initials: LL
authors.lastname: Chen
authors.forename: C V
authors.initials: CV
authors.lastname: Dang
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D016466:CHO Cells; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D006224:Cricetinae; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000235:genetics / Q000378:metabolism; D010449:Peptide Mapping; D010957:Plasmids / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C052130:GAL4 protein, S cerevisiae; D046911:Macromolecular Substances; C067850:Myc associated factor X; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D016271:Proto-Oncogene Proteins c-myc; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D015500:Chloramphenicol O-Acetyltransferase