DIFFERENTIAL-EFFECTS OF MAX PROTEINS (LONG AND SHORT) ON GROWTH AND DIFFERENTIATION OF MURINE ERYTHROLEUKEMIA-CELLS

The myc gene product belongs to a family of basic, Helix-Loop-Helix, L eucine Zipper (b-HLH-LZ) proteins involved in cell growth, differentia tion and tumorigenesis. The Max protein dimerizes with Myc to form a c omplex which binds to DNA and promotes transcription of target genes. Max exists in two major forms, Max-9 (long) and Max (short), which dif fer by 9 amino acids just amino to the basic region. We compared the i n vivo behavior of the two forms in stable transfectants of long and s hort wild type (Lwt, Swt) and basic region mutants (Lbm, Sbm). While b oth Lwt-max and Swt-max clones exhibit delays in cell growth and diffe rentiation, these delays are far more pronounced in the Lwt-max clones . In contrast, no difference is noted between Lbm-Max and Sbm-Max in t heir observed ability to delay growth, to accelerate HMBA-induced diff erentiation and to induce spontaneous differentiation. We suggest that a difference in affinity for DNA underlies the differential activitie s of Lwt- and Swt-Max.