I To whom requests for reprints should be addressed. Regions within the c-Myc Protein That Are Necessary for Transformation Are Also Required for Inhibition of

The c-, L-, and N-Myc nuclear phosphoproteins share several highly conserved regions that partially overlap putative fundional domains of the c-Myc protein. All three myc oncogenes can cooperate with an adivated ras gene to transform primary rat embryo cells (REC), and deregulated expression of c- and L-myc can block differentiation of murine erythroleukemia (MEL) cells. In the present study, we demonstrate that N-myc also can block MEL cell differentiation, and we identify regions within the c-Myc protein that are necessary for inhibition of MEL differentiation. C19 MEL cells were transfeded with six human c-myc genes which were partially deleted in different areas of the coding region. Four of the genes lack sequences that overlap either the putative transcriptional activation domain, the helix-loop-helix motif, or the leucine zipper motif and were previously shown to have lost REC cotransformin