title: Determination of sequences responsible for the differential regulation of Myc function by delta Max and Max.
abstract: The DNA-binding, transcriptional activation and transforming activities of the Myc protein require dimerization with Max. Max can form also homodimers which are able to bind the same DNA sequence as Myc/Max heterodimers and suppress Myc-induced transcription and transformation. We have recently identified a naturally occurring truncated form of Max, delta Max, which in a rat embryo fibroblast enhances transformation by Myc and Ras. Like Max, this delta Max protein contains a b-HLH-Zip domain, except that the end of the leucine zipper is replaced by five delta Max-specific amino acid residues. Delta Max also lacks the C-terminal sequences of Max including a nuclear localisation signal. Here we have dissected the regions responsible for the specific effects of Max and delta Max in Ras-Myc cotransformation of rat embryo fibroblasts. Our results indicate that the suppressive activity of Max requires C-terminal acidic and basic regions and an intact leucine zipper. Replacement of the end of the leucine zipper with the delta Max-specific sequence is responsible for the enhancement of transformation by delta Max. Surprisingly, delta Max does not require the DNA-binding basic region for enhancement of transformation and has no effect on Myc-induced transcription activation from Myc/Max-binding site-containing promoter construct.
authors.affiliation: Molecular/Cancer Biology Laboratory, Haartman Institute, University of Helsinki, Finland.
authors.forename: I
authors.initials: I
authors.lastname: Västrik
authors.forename: T P
authors.initials: TP
authors.lastname: Mäkelä
authors.forename: P J
authors.initials: PJ
authors.lastname: Koskinen
authors.forename: K
authors.initials: K
authors.lastname: Alitalo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000502:physiology; D018257:Helix-Loop-Helix Motifs; D066298:In Vitro Techniques; D016350:Leucine Zippers; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000502:physiology*; D051381:Rats; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014157:Transcription Factors / Q000737:chemistry* / Q000502:physiology
chemical_list: D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; C499329:Max protein, rat; C067850:Myc associated factor X; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors