Abstract
Starved cells of Dictyostelium discoideum begin to synthesize a new class of developmentally regulated proteins at about 13 hr of the 24-hr developmental program, concomitant with the formation of tips on the tight cell aggregates [Alton, T. H. & Lodish, H. F. (1977) Dev. Biol. 60, 180--206]. Continued synthesis of these proteins is normally dependent upon the integrity of the multicellular aggregates, because cells that have been disaggregated at 13 hr and shaken in suspension for 5 hr do not make these proteins. We show here that addition of 20 microM cyclic AMP to suspension cultures of disaggregated 13-hr cells caused synthesis of most of these late proteins to be maintained. Translation in an in vitro wheat germ system of total cellular RNA isolated from these cyclic AMP-stimulated suspension cells, or from normal aggregates, generated several proteins that were not encoded by the RNA isolated from equivalent suspension cells which had not been treated with cyclic AMP or from preaggregation cells. We conclude that cyclic AMP has a direct role in maintaining the synthesis of aggregation-dependent Dictyostelium proteins and in maintaining the level of the corresponding mRNAs.