Molecular and genetic analyses of the nimO initiator of DNA synthesis in Aspergillus nidulans.

Steven W. James, Karen E. Messner, and Maureen C. Miller.


The nimO gene of Aspergillus nidulans shares structural and functional homology with the budding yeast G1/S regulator, Dbf4, being required both for initiation of DNA synthesis and efficient progression through S phase; and involved in a checkpoint linking DNA synthesis with mitosis (James et al., accepted; 19th FGC). The gene is essential, because strains containing alcA:: nimO+ as their only copy of nimO become completely ethanol-dependent. Since the greatest similarity between nimO and Dbf4 lies in their C-termini, nimO function was investigated using a series of alcA-driven C-terminal truncations. nimO alleles lacking as much as 244 C terminal amino acids partially rescued nim018 ts-lethality when expression was strongly induced, by permitting vegetative growth but not asexual development. However, these truncated alleles could not complement a deletion of nim0, indicating that the C-terminus is essential and suggesting that the nim018 protein and truncated polypeptides somehow interact. Dbf4p triggers DNA synthesis by activating the Cdc7p kinase and escorting it to targets at origins of replication. If nimO is a Dbf4 homolog, it should associate with its cognate Aspergillus partner. We isolated and sequenced an apparent Aspergillus homolog of Cdc7 (Cdc7Asp), and we have identified two new loci, snoA and snoB, as partial suppressors of nim018. Preliminary studies using Cdc7Asp suggest that it may complement snoA suppressors, and molecular and genetic studies are underway to ascertain if (1) snoA encodes Cdc7Asp, and if (2) nimOp and Cdc7pAsp physically associate to control , DNA synthesis. (Supported by NSF-RUI# MCB 95-07485).

abstract No: 

Fungal Genet. Newsl. 46 (Supl):

Full conference title: 

Fungal Genetics Conference 20th
    • Fungal Genetics Conference 20th (1999)