BimD/SPO76 is at the interface of cell cycle progression, chromosome morphogenesis, and recombination

BIMD of Aspergillus nidulans belongs to a highly conserved protein family i mplicated, in filamentous fungi, in sister-chromatid cohesion and DNA repai r. We show here that BIMD is chromosome associated at all stages, except fr om late prophase through anaphase, during mitosis and meiosis, and is invol ved in several aspects of both programs. First, bimD(+) function must be ex ecuted during S through M. Second, in bimD6 germlings. mitotic nuclear divi sions and overall cellular program occur more rapidly than in wild type. Th us, BIMD, an abundant chromosomal protein, is a negative regulator of norma l cell cycle progression. Third, bimD6 reduces the level of mitotic interho molog recombination but does not alter the ratio between crossover and nonc rossover outcomes. Moreover, bimD6 is normal for intrachromosomal recombina tion. Therefore, BIMD is probably not involved in the enzymology of recombi national repair per se. Finally, during meiosis, staining of the Sordaria o rtholog Spo76p delineates robust chromosomal axes, whereas BIMD stains all chromatin. SPO76 and bimD are functional homologs with respect to their rol es in mitotic chromosome metabolism but not in meiosis. We propose that BIM D exerts its diverse influences on cell cycle progression as well as chromo some morphogenesis and recombination by modulating chromosome structure.