The filamentous fungus Aspergillus nidulans forms septa in order to partition portions of an extending germ tube thus cellularizing the resultant mycelia. Septum formation is temporally and spatially regulated by nuclear positioning and cell cycle progression. sepHl was identified in a conditional mutant screen for cytokinesis mutants. At restrictive temperature sepHl mutants polarize a germ tube and undergo many rounds of nuclear division but fail to form septa. Septum formation is reversible in sepHl mutants when they are returned to percussive temperature, but remains blocked if nuclei are prevented from traversing mitosis. SEPH is a 165kD ser/thr protein kinase. SepH is 42% identical and 62% similar to cdc7, a gene required for septum formation in S. pombe. Targeted disruption of the sepH gene results in a strain (seph::argB) which is unable to form septa at any temperature. Interestingly, the disruption strain displays a thermosensitive-lethal phenotype with cells accumulating defects observed as aberrant nuclear morphology at 42 C. A screen for suppressors of this thermosensitve phenotype has yielded a pool of seph::argB/mutant strains that are viable at 42 C and capable of forming septa. Termed BSH for by-pass sepH, the phenotype of these suppressors may offer some insight into sepH function. Bshl67 is temperature sensitive and produces uninucleate sub-apical cells. This phenotype is strikingly similar to that of a strain highly expressing the S.pombe cdc7 gene under the control of the inducible AIcA promoter. SepH and cdc7 represent an emerging class of protein kinases involved in cytokinesis.
Fungal Genet. Newsl. 46 (Supl):
Full conference title:
Fungal Genetics Conference 20th
- Fungal Genetics Conference 20th (1999)