SEPB of Aspergillus nidulans is a conserved protein which functions to maintain genome stabilit

Scott E. Gygax, Amy Hofmann, and Steven D. Harri

Author address: 

Dept. of Microbiology, University of Connecticut Health Center, Farmington, CT. 06030-320


A temperature sensitive mutation in the Aspergillus nidulans sepB gene dramatically perturbs chromosomal DNA metabolism. At restrictive temperature, this mutation causes; i) elevated levels of mitotic recombination, ii) enhanced levels of chromosomal loss, iii) progressive delays in nuclear division, and iv) the formation of morphologically aberrant interphase nuclei. Molecular characterization of the sepB gene demonstrates that it encodes a 837 amino acid predicted protein possessing five N-terminal consensus WD-40 repeats, a C-terminal Helix-Loop-Helix motif, and a motif shared with DNA polymerase a. Upon sequencing the sepB3 mutant allele, we identified a single missense mutation (P618S) in a conserved proline residue preceding the C- terminal HLH motif, suggesting that the structural stability of this motif might be essential to its function. Protein sequence homology suggests that SEPB might be a member of a conserved family of proteins (S. cerevisiae Ctf4p, X. laevis AND-1, and H. sapiens hAND-1) required for the maintenance of genome stability. ctf4 mutants have a similar genome instability phenotype, and it has been shown that Ctf4p physically binds to DNA polymerase a suggesting a replication function. We are currently assessing the level of functional conservation within the SEPB family of proteins by testing the ability of hAND-1 and Ctf4p to complement the sepB3 mutant. Phenotypic characterization of sepB3 double mutants in backgrounds defective in the DNA damage checkpoint (uvsB110, uvsD153, nimXcdc2AF) or DNA recombination (nuv2, nuv4, nuv8, and musN227) revealed several synthetic interactions. The sepB3 mutation also causes an elevated level of both spontaneous and induced mutagenesis at the permissive temperature. Phenotypic characterization of sepB3 double mutants with a hyper-recombinatory mutation such as musN227 (RecQ helicase) demonstrated an increase in mutagenesis compaired to sepB3 alone suggesting that the increased mutagenesis is dependent upon recombination. At semi-permissive temperature, the sepB3 mutation causes enhanced sensitivity to MMS and bleomycin. These data suggest that the SEPB protein family might have a role in DNA replication during S-phase as well the repair of double-strand breaks (DSBs)

abstract No: 


Full conference title: 

21st Fungal Genetics Conference
    • Fungal Genetics Conference 21st (2000)