STRUCTURAL AND FUNCTIONAL ARCHITECTURE OF THE YEAST CELL-CYCLE TRANSCRIPTION FACTOR SWI6

The structural and functional organisation of Swi6, a transcriptional regulator of the budding yeast cell cycle has been analysed by a combi nation of biochemical, biophysical and genetic methods. Limited proteo lysis indicates the presence of a similar to 15 kDa N-terminal domain which is dispensable for Swi6 activity in vivo and which is separated from the rest of the molecule by an extended Linker of at least 43 res idues. Within the central region, a 141 residue segment that is capabl e of transcriptional activation encompasses a structural domain of app roximately 85 residues. In turn, this is tightly associated with an ad jacent 28 kDa domain containing at least four ankyrin-repeat (ANK) mot ifs. A second protease sensitive region connects the ANK domain to the remaining 30 kDa C-terminal portion of Swi6 which contains a second t ranscriptional activator and sequences required for heteromerisation w ith Swi4 or Mbp1. Transactivation by the activating regions of Swi6 is antagonised when either are combined with the central ankyrin repeat motifs. Hydrodynamic measurements indicate that an N-terminal 62 kDa f ragment comprising the first three domains is monomeric in solution an d exhibits an unusually high frictional coefficient consistent with th e extended, multidomain structure suggested by proteolytic analysis. ( C) 1998 Academic Press.