ID HELIX-LOOP-HELIX PROTEINS IN CELL-GROWTH AND DIFFERENTIATION

Id helix-loop-helix proteins function at a general level as positive r egulators of cell growth and as negative regulators of cell differenti ation. They act as dominant-negative antagonists of other helix-loop-h elix transcription factors, which drive cell lineage commitment and di fferentiation in diverse cell types of higher eukaryotes. In addition, the functions of Id proteins are integrated with cell-cycle-regulator y pathways orchestrated by cyclin-dependent kinases and the retinoblas toma protein. Here, some of the recent advances that highlight the imp ortance of Id proteins as regulatory intermediates for coordinating di fferentiation-linken gene expression with cell-cycle control in respon se to extracellular signalling are reviewed.