DETERMINATION OF SEQUENCES RESPONSIBLE FOR THE DIFFERENTIAL REGULATION OF MYC FUNCTION BY DELTA-MAX AND MAX

: VÄSTRIK I, MÄKELÄ TP, KOSKINEN PJ, ALITALO K

Publisher: STOCKTON PRESS

: 1995

: Oncogene

: ONCOGENE

: 11

: 3

: 553

: 560

: 8

: 0950-9232

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 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.