REGULATION OF TRANSCRIPTION FACTOR LOCALIZATION - FINE-TUNING OF GENE-EXPRESSION

Import of 'nuclear' proteins into the nucleus, in particular, transcri ption factors, is not a constitutive process; instead it appears to be modulated in response to external stimuli, cell-cycle progression and developmental cues. Examples of such regulation involve direct phosph orylation of the transported protein, masking of the nuclear localizat ion signal(s), cytoplasmic retention by binding to an anchoring protei n, modulation of the import machinery itself and possible interplay be tween these different mechanisms. As such, nucleo-cytoplasmic traffic constitutes an important regulatory checkpoint in the control of gene expression.