G{alpha}5 subunit-mediated signalling requires a D-motif and the MAPK ERK1 in Dictyostelium

Department of Microbiology and Molecular Genetics, Oklahoma State University, Stillwater, OK 74078-3020, USA The Dictyostelium G 5 subunit has been shown to reduce cell viability, inhibit folate chemotaxis and accelerate tip morphogenesis and gene expression during multicellular development. Alteration of the D-motif (mitogen-activated protein kinase docking site) at the amino terminus of the G 5 subunit or the loss of extracellular signal-regulated kinase (ERK)1 diminished the lethality associated with the overexpression or constitutive activation of the G 5 subunit. The amino-terminal D-motif of the G 5 subunit was also found to be necessary for the reduced cell size, small aggregate formation and precocious developmental gene expression associated with G 5 subunit overexpression. This D-motif also contributed to the aggregation delay in cells expressing a constitutively active G 5 subunit, but the D-motif was not necessary for the inhibition of folate chemotaxis. These results suggest that the amino-terminal D-motif is required for some but not all phenotypes associated with elevated G 5 subunit functions during growth and development and that ERK1 can function in G 5 subunit-mediated signal transduction. Correspondence Jeffrey A. Hadwiger jeff.hadwiger{at}okstate.edu Abbreviations: ERK, extracellular signal-regulated kinase; MAPK, mitogen-activated protein kinase Present address: W. M. Keck Dynamic Image Analysis Facility, University of Iowa, 014 Biology Building East, Iowa City, IA 52242, USA. A supplementary table showing the selection of g 5 transformants is available with the online version of this paper.