The mechanisms controlling gene regulation appear to be fundamentally different in eukaryotes and prokaryotes (Struhl (1999) CELL, 98, 1-4). To investigate this diversity further, we have analysed the distribution of all known transcription-associated proteins (TAPs), as reflected by sequence database annotations. Our results for the primary phylogenetic domains (Archaea, Bacteria and Eukaryota) show that TAP families are mostly taxon-specific and very few transcriptional regulators are common across these domains.