EXPRESSION OF A CONSTITUTIVELY ACTIVE CA2+ CALMODULIN-DEPENDENT KINASE IN ASPERGILLUS-NIDULANS SPORES PREVENTS GERMINATION AND ENTRY INTO THE CELL-CYCLE/

The unique gene for Ca2+/calmodulin-dependent protein kinase (CaMK) ha s been shown to be essential in Aspergillus nidulans. Disruption of th e gene prevents entry of spores into the nuclear division cycle. Here we show that expression of a constitutively active form of CaMK also p revents spores from entering the first S phase in response to a germin ating stimulus. Expression of the constitutively active kinase induces premature activation of NIME(cyclin B)/NIMX(cdc2) in G(0)/G(1). As NI MX(cdc2) is present in spores, the elevation of maturation promotion f actor activity may be secondary to the early production of NIME(cyclin B) or post-translation modification of maturation promotion factor. T he expression of the constitutively active CaMK also results in the ap pearance of NIMA kinase activity within 1 h of the germinating signal. These results support the contention that the activities of maturatio n promotion factor and NIMA are coincidentally regulated in A. nidulan s and suggest that the unscheduled appearance of one or both of these activities may be sufficient to prevent A, nidulans spores from enteri ng into DNA synthesis.