DOMAINS OF P85(CDC10) REQUIRED FOR FUNCTION OF THE FISSION YEAST DSC-1 FACTOR

p85cdc10 is a component of the S.pombe DSC-1 complex, which is thought to mediate periodic transcription of genes in late G1. In order to un derstand the role of p85cdc10 in the function of this complex, we have analysed which domains of p85cdc10 are required for biological activi ty and the formation of a stable DSC-1 complex in vitro, both in cdc10 temperature sensitive and null backgrounds. No DSC-1 activity is foun d in the absence of p85cdc10 and the activity of the complex is reduce d or absent in all cdc10ts mutants tested. Full biological activity an d rescue of a cdc10::ura4+ null allele requires the N-terminal domain, the cdc10/SWI6 repeats and the helical C-terminal region. In the abse nce of p85cdc10, both the C-terminal and cdc10/SWI6 repeat domains are required for DSC-1 activity in vitro. In a cdc10ts background, rescue of DSC-1 activity and complementation of mutants, requires only expre ssion of the C-terminal domain, though the presence of the cdc10/SWI6 motifs enhances its activity. The N-terminal domain, alone, or in comb ination with the cdc10/SWI6 motifs, does not have biological activity, and does not restore DSC-1 activity. We conclude that both the C-term inal domain of p85cdc10 is critical for formation of the DSC-1 complex and that the cdc10/SWI6 motifs also play a role, perhaps by stabilizi ng the complex. Our data also suggest that the S.pombe DSC-1 complex c ontains more than one molecule of p85cdc10.