Transcription factor CCTF1 plays an important role in regulating proteasome activity during archaeal cell division

Archaea of the order Sulfolobales exhibit a highly ordered cell cycle progression similar to that of eukaryotes. It has been demonstrated that degradation of the cell division protein CdvB by the proteasome controls the progression of cell division. However, how the proteasome itself is regulated during the cell cycle is not fully understood. Recently, the cyclically expressed ArsR (arsenical resistance operon repressor) family transcription factor CCTF1 (cell cycle transcription factor 1) was shown to repress expression of PAN (proteasome-activating nucleotidase) in Sulfolobus acidocaldarius. Here, using biochemical approaches, comparative transcriptomics, and proteomics, we provide further insights into the CCTF1 function and show that it regulates PAN expression in Saccharolobus islandicus by binding to an AT-rich palindromic sequence within the pan promoter. We also reassessed the role of the cyclically expressed protein kinase aCcrK in the regulation of proteasome activity and conclude that CCTF1, rather than aCcrK, is the primary factor controlling the proteasome activity. These findings advance our understanding of the proteasome-mediated cell cycle regulation in archaea.