The development of increasingly sophisticated tools to track chromosomes and proteins in living cells offers the possibility of visualising gene regulation in the nucleus with minimal distortion. This, in conjunction with powerful genetic approaches available in yeast, is beginning to allow functional definition of nuclear "compartments".
Lymphocyte Development Group, Medical Research Council, Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK.