THE CALMODULIN-DEPENDENT PROTEIN PHOSPHATASE CATALYTIC SUBUNIT (CALCINEURIN-A) IS AN ESSENTIAL GENE IN ASPERGILLUS-NIDULANS

The gene encoding the homologue of the catalytic subunit of the Ca2+/calmodulin-regulated protein phosphatase 2B (calcineurin A) has been isolated from Aspergillus nidulans. This gene, cna(A+), is essential in this fungal system. Analysis of growth-arrested cells following gene disruption by homologous recombination reveals that they are blocked early in the cell cycle. The cna(A+) gene encodes a 2.5 kb mRNA and the deduced protein sequence is highly homologous to the calcineurin A subunit of other species. The mNRA varies in a cell cycle-dependent manner with maximal levels found early in G(1) and considerably before the G(1)/S boundary. As calmodulin is also essential for A.nidulans cell cycle progression and levels rise before the G(1)/S boundary, our data suggest that calcineurin may represent a primary target for calmodulin at this cell cycle transition point.