Specific expression of a gene encoding a novel calcium-binding protein, CAF-1, during transition of Dictyostelium...

The gene expressions involved in the transition from cell proliferation to differentiation were analyzed, using synchronized Dictyostelium discoideum Ax-2 cells and the differential plaque hybridization method. As one of the genes (cDNA) specifically expressed when Ax-2 cells were starved just before the putative shift (PS)-point (putative shift point; a switchover point from growth to differentiation in the cell cycle), calfumirin-1 (CAF-1) was cloned, which encoded a novel calcium-binding protein with E-F hand. Although CAF-1 mRNA was slightly expressed in vegetatively growing cells, the expression was markedly increased in response to starvation of cells just before the PS-point. Northern analysis using non-synchronized Ax-2 cells showed that the CAF-1 mRNA is predominantly expressed within a few hours of starvation. Such a starvation-induced early expression of the CAF-1 mRNA raised a possibility that CAF-1 might be one of Ca2+ -binding proteins involved in the phase-shift of cells from growth to differentiation.