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Max is a basic helix-loop-helix/leucine zipper (bHLH/LZ) protein that forms sequence-specific DNA-binding complexes with the c-Myc oncoprotein (Myc). Using Saccharomyces cerevisiae, we have shown that the Max bHLH/LZ domain enables Myc to activate transcription through CACGTG and CACATG sequences in vivo, and that the number and context of such sites determines the level of activation. In addition, we have used yeast to investigate the role of the Myc helix-loop-helix (HLH) and leucine zipper (LZ) motifs in mediating Max-dependent DNA-binding and transcriptional activation in vivo using HLH/LZ mutants generated by site-directed mutagenesis. The results show that, while both motifs are essential for Myc to activate transcription, helix 2 of the HLH together with the contiguous LZ suffice to mediate complex formation with Max, whilst helix 1 is essential for sequence-specific DNA binding of Myc-Max complexes. Furthermore, the ability of Myc HLH/LZ mutants to bind DNA and activate transcription in collaboration with Max correlates closely with their neoplastic transforming activity in higher eukaryotic cells.

Type

Journal article

Journal

Oncogene

Publication Date

07/1993

Volume

8

Pages

1849 - 1855

Addresses

Cancer Research Campaign Beatson Laboratories, Beatson Institute for Cancer Research, Bearsden, Glasgow, UK.

Keywords

Saccharomyces cerevisiae, Cell Transformation, Neoplastic, DNA-Binding Proteins, Proto-Oncogene Proteins c-myc, Transcription Factors, DNA, Base Sequence, Protein Structure, Secondary, Leucine Zippers, Mutation, Molecular Sequence Data, Basic-Leucine Zipper Transcription Factors, Transcriptional Activation