The ‘BN2’ gene, a regulator for the onset of chromosome condensation

This review deals with the condensation–decondensation cycle of chromatin. This cycle can be analysed in increasing detail because of the availability of well‐characterized temperature‐sensitive cell‐cycle mutants in which the control for condensation is aberrant at the non‐permissive temperature. DNA transfection and gene cloning techniques using one such mutant have resulted in the identification of a gene involved in the normal regulation of entry into mitosis.