Expression of a cAMP receptor gene of Dictyostelium and evidence for a multigene family

We have previously reported the cloning of cDNAs for a Dictyostelivm cell-surface cAMP receptor that is a member of the family of G-protein-linked receptors. Here, we report the organization and the developmental expression of this cAMP receptor gene, designated CAR1. CAR1 is a single copy gene that contains two intervening sequences. CAR1 mRNA levels are low in growing cells, rise to peak expression at 5-10 hr of development when the cAMP signaling system is maximally active, and decrease as development proceeds. At 5 hr the predominant mRNA species is ∼1.9 kb, by 10 hr the mRNA is heterogeneous with sizes of ∼1.9-2.1 kb, but during culmination only the 2.1 kb mRNA is detected. The variety of mRNA sizes results from differences in 5′-untranslated regions. Studies using developmental mutants with aberrant cAMP-signaling patterns indicate that pulsatile action of cAMP promotes maximal expression of CAR1 during early development. Low stringency hybridization of CAR1 probes to genomic DNA detects additional, related sequences, suggesting that there are several genes that encode a family of structurally similar receptors. Multiple functions previously attributed to the cAMP receptor instead may be fulfilled by distinct receptor subtypes encoded by specific genes.