Oncogene-encoded proteins c-Myc, N-Myc, and L-Myc function in cell proliferation, differentiation and neoplastic disease. Amplification of the c-Myc gene has been found in several types of human tumors, the N-Myc gene in neuroblastomas, and the L-Myc gene in human small cell lung carcinomas. c-Myc protein is a transcription factor localized to the nucleus of the cell. It seems to be involved in activating the transcription of growth-related genes. c-Myc binds to DNA during transcription as a heterodimeric complex with Max. c-Myc is phosphorylated in vitro by p44/42 MAP kinase at Ser62 and in vivo at both Thr58 and Ser62. Mutation of Thr58 and Ser62 to Ala inhibits the ability of c-Myc to activate transcription.