Opinion - Analysis of genomic targets reveals complex functions of MYC

MYC is overexpressed by many human tumour types and has been shown to regulate cell functions that are required for tumorigenesis. It is not clear, however, which of its target genes mediate these effects. A series of recent studies have indicated that this could be a result of the fact that MYC binds and regulates up to 15% of all genes. Does MYC function as a widespread regulator of transcription or as a classical transcription factor that regulates a limited number of downstream targets?