Evidence for domain organization within the 61-kDa calmodulin-dependent cyclic nucleotide phosphodiesterase from bovine brain

The complete amino acid sequence of the 61-kDa calmodulin-dependent, cyclic nucleotide phosphodiesterase (CaM-PDE) from bovine brain has been determined. The native protein is a homodimer of N alpha-acetylated, 529-residue polypeptide chains, each of which has a calculated molecular weight of 60,755. The structural organization of this CaM-PDE has been investigated with use of limited proteolysis and synthetic peptide analogues. A site capable of interacting with CaM has been identified, and the position of the catalytic domain has been mapped. A fully active, CaM-independent fragment (Mr = 36,000), produced by limited tryptic cleavage in the absence of CaM, represents a functional catalytic domain. N-Terminal sequence and size indicate that this 36-kDa fragment is comprised of residues 136 to approximately 450 of the CaM-PDE. This catalytic domain encompasses a approximately 250 residue sequence that is conserved among PDE isozymes of diverse size, phylogeny, and function. CaM-PDE and its PDE homologues comprise a unique family of proteins, each having a catalytic domain that evolved from a common progenitor. A search of the sequence for potential CaM-binding sites revealed only one 15-residue segment with both a net positive charge and the ability to form an amphiphilic alpha-helix. Peptide analogues that include this amphiphilic segment were synthesized. Each was found to inhibit the CaM-dependent activation of the enzyme and to bind directly to CaM with high affinity in a calcium-dependent manner. This site is among the sequences cleaved from a 45-kDa chymotryptic fragment that has the complete catalytic domain but no longer binds CaM. These results indicate that residues located between position 23 and 41 of the native enzyme contribute significantly to the binding of CaM although the involvement of residues from additional sites is not excluded.

Sequence comparison of the 63-, 61-, and 59-kDa calmodulin-dependent cyclic nucleotide phosphodiesterases

Partial protein sequences from the 59-kDa bovine heart and the 63-kDa bovine brain calmodulin-dependent phosphodiesterases (CaM-PDEs) were determined and compared to the sequence of the 61-kDa isozyme reported by Charbonneau et al. [Charbonneau, H., Kumar, S., Novack, J. P., Blumenthal, D. K., Griffin, P. R., Shabanowitz, J., Hunt, D. F., Beavo, J. A. & Walsh, K. A. (1991) Biochemistry (preceding paper in this issue)]. Only a single segment (34 residues) at the N-terminus of the 59-kDa isozyme lacks identity with the 61-kDa isozyme; all other assigned sequence is identical in the two isozymes. Peptides from the 59-kDa isozyme that correspond to residues 23-41 of the 61-kDa protein bind calmodulin with high affinity. The C-terminal halves of these calmodulin-binding peptides are identical to the corresponding 59-kDa sequence; the N-terminal halves differ. The localization of sequence differences within this single segment suggests that the 61- and 59-kDa isozymes are generated from a single gene by tissue-specific alternative RNA splicing. In contrast, partial sequence from the 63-kDa bovine brain CaM-PDE isozyme displays only 67% identity with the 61-kDa isozyme. The differences are dispersed throughout the sequence, suggesting that the 63- and 61-kDa isozymes are encoded by separate but homologous genes.

Attenuation of cAMP-mediated responses in MA-10 Leydig tumor cells by genetic manipulation of a cAMP-phosphodiesterase

In order to assess the effect of increased cAMP degradation on the responsiveness on an endocrine cell, we have obtained stable transfectants of MA-10 Leydig tumor cells that overexpress a mammalian cAMP-phosphodiesterase. Two novel cell lines, designated MA-10(P+8) and MA-10(P+29), that express high levels of the transfected enzyme were characterized. Although the basal levels of cAMP in the mutant cell lines are comparable to those of the wild-type cells, the increase in cAMP accumulation elicited by human choriogonadotropin (hCG) is severely blunted. Further studies with MA-10(P+29) show that the ability of hCG to stimulate adenylyl cyclase activity is normal. The failure of MA-10(P+29) cells to accumulate cAMP in response to hCG can be correlated with a similar reduction in hCG-stimulated steroidogenesis. On the other hand, the maximal steroidogenic response of MA-10(P+29) cells to dibutyryl cAMP, a cAMP analogue that is fairly resistant to phosphodiesterase degradation, is normal. We also show that the ability of these cells to respond to hCG with increased cAMP accumulation and steroid synthesis can be restored with a specific phosphodiesterase inhibitor. These results demonstrate that overexpression of a cAMP-phosphodiesterase in MA-10 cells limits the levels of cAMP attained under hCG stimulation and supresses the steroidogenic response of these cells to hCG. Since gonadotropins increase the cAMP-phosphodiesterase activity in their target cells, these findings also provide evidence that this regulation plays a major role in the modulation of cell responsiveness. Last, these new cell lines should be valuable in the study of the actions of cAMP because they express a conditional and reversible cAMP-resistant phenotype.

The Drosophila dunce locus: learning and memory genes in the fly

The dunce gene, one of several genes critical for normal learning and memory in Drosophila, is organized in a complex and bizarre way, with enormous introns containing several other unrelated genes. Recent studies have focused on the spatial expression pattern of the product, cAMP phosphodiesterase, and have provisionally identified the mushroom bodies as important sites of action of dunce within adult brain. In addition, the recent cloning and characterization of dunce counterparts from mammals has revealed that these too may participate in animal behavior and, in particular, in the regulation of mood.

Expression of three mammalian cDNAs that interfere with RAS function in Saccharomyces cerevisiae

Saccharomyces cerevisiae strains expressing the activated RAS2Val19 gene or lacking both cAMP phosphodiesterase genes, PDE1 and PDE2, have impaired growth control and display an acute sensitivity to heat shock. We have isolated two classes of mammalian cDNAs from yeast expression libraries that suppress the heat shock-sensitive phenotype of RAS2Val19 strain. Members of the first class of cDNAs also suppress the heat shock-sensitive phenotype of pde1- pde2- strains and encode cAMP phosphodiesterases. Members of the second class fail to suppress the phenotype of pde1- pde2- strains and therefore are candidate cDNAs encoding proteins that interact with RAS proteins. We report the nucleotide sequence of three members of this class. Two of these cDNAs share considerable sequence similarity, but none are clearly similar to previously isolated genes.

Differential regulation of myelin gene expression in SV40 T antigen-transfected rat glioma C6 cells

Rat glioma C6 cells were stably transfected with a pSV3-neo plasmid containing SV40 T antigen gene, and geniticin-resistant transfectants (designated C6T cells) were cloned. The C6T cells grew as well-defined foci of cells showing squamous or irregular morphology. The doubling time for transfected cells was reduced by approximately 40% as compared to control C6 cells. The transfection with T-antigen also affected the expression of genes coding for structural myelin proteins and for myelin-associated enzymes. The steady-state level of proteolipid protein (PLP)-specific mRNA in C6T cells was 44% lower than in parental C6 cells. On the other hand, the transfection upregulated the expression of myelin-associated glycoprotein (MAG) by 153%. The activity of 2':3' cyclic AMP phosphodiesterase (CNP) was increased by approximately 80% in the C6T cells as compared to untransfected, control cells. The activity of calcium-activated neutral proteinase (CANP) was also significantly elevated in the transfectants by approximately 50% and 220% for millimolar and micromolar form respectively. The results indicate that T antigen affects the expression of myelin genes, although, individual genes appear to be differently regulated implying the existence of several independent regulatory mechanisms.

The cyclic AMP phosphodiesterase encoded by the Drosophila dunce gene is concentrated in the mushroom body neuropil

Drosophila dunce (dnc) flies are defective in learning and memory as a result of lesions in the gene that codes for a cAMP-specific phosphodiesterase (PDE). Antibodies to the dnc PDE showed that the most intensely stained regions in the adult brain were the mushroom body neuropil--areas previously implicated in learning and memory. In situ hybridization demonstrated that dnc RNA was enriched in the mushroom body perikarya. The mushroom bodies of third instar larval brains were also stained intensely by the antibody, suggesting that the dnc PDE plays an important role in these neurons throughout their development. The role of the dnc PDE in mushroom body physiology is discussed, and a circuit model describing a possible role of the mushroom bodies in mediating olfactory learning and memory is presented.

Expression of human recombinant cAMP phosphodiesterase isozyme IV reverses growth arrest phenotypes in phosphodiesterase-deficient yeast

The low-Km cAMP-specific phosphodiesterases (PDEases) are of great pharmacological significance because of their involvement in regulating cAMP concentrations, which, in turn, are responsible for mediating the cellular response to extracellular signals such as hormones and neurotransmitters. We recently reported the isolation of a cDNA clone that encodes a human monocyte low-Km, rolipram-sensitive, cAMP PDEase (isozyme IV). We have engineered the inducible expression of this human PDEase in yeast. Cells of Saccharomyces cerevisiae contain two genes that encode cAMP PDEases. PDEase-deficient mutants are viable but exhibit specific growth arrest phenotypes associated with elevated intracellular cAMP content; these phenotypes include heat shock sensitivity and the inability to grow on acetate as a carbon source. We show that functional expression of our human cAMP PDEase in a genetically engineered PDEase-deficient strain of S. cerevisiae reverses these aberrant phenotypes. Furthermore, under conditions for growth arrest, rolipram is cytotoxic to PDEase-deficient mutants expressing the human cAMP PDEase, indicating that it is capable of inhibiting the human recombinant enzyme in vivo. This system can be used in the development of a yeast cell-based assay for isozyme-selective inhibitors of the human recombinant cAMP PDEase.

Cyclic nucleotide phosphodiesterase of Dictyostelium discoideum and its glycoprotein inhibitor: structure and expression of their genes

The genes coding for the cyclic nucleotide phosphodiesterase (PD) and the PD inhibitory glycoprotein (PDI) have been cloned and characterized. The PDI gene was isolated as a 1.6 kb genomic fragment, which included the coding sequence containing two small introns and 510 nucleotides of non-translated 5' sequence. From the deduced amino acid sequence we predict a protein with a molecular weight (MW) of 26,000 that, in agreement with previous data, contains 15% cysteine residues. Genomic Southern blot analysis indicates that only one gene encodes the inhibitor. Northern blot analysis shows a single transcript of 0.95 kb. The PDI gene is expressed early in development with little transcript remaining following aggregation. The appearance of PDI mRNA is prevented by the presence of cAMP, but when cAMP is removed the transcript appears within 30 minutes. When cAMP is applied to cells expressing PDI the transcript disappears with a half-life of less than 30 minutes. The PD gene of D. discoideum is transcribed into three mRNAs: a 1.9 kb mRNA specific for growth, a 2.4 kb mRNA specific for aggregation, and a 2.2 kb mRNA specific for late development. The 2.2 kb mRNA is also specific for prestalk cells, and is induced by differentiation-inducing factor. All three mRNAs contain the same coding sequence, and differ only in their 5' non-coding sequences. Each mRNA is transcribed from a different promoter, and by using the chloramphenicol acyltransferase gene as a reporter, we have shown that each promoter displays the same regulation as its cognate mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Cloning and expression of cDNA for a human low-Km, rolipram-sensitive cyclic AMP phosphodiesterase

We have isolated cDNA clones representing cyclic AMP (cAMP)-specific phosphodiesterases (PDEases) from a human monocyte cDNA library. One cDNA clone (hPDE-1) defines a large open reading frame of ca. 2.1 kilobases, predicting a 686-amino-acid, ca. 77-kilodalton protein which contains significant homology to both rat brain and Drosophila cAMP PDEases, especially within an internal conserved domain of ca. 270 residues. Amino acid sequence divergence exists at the NH2 terminus and also within a 40- to 100-residue domain near the COOH-terminal end. hPDE-1 hybridizes to a major 4.8-kilobase mRNA transcript from both human monocytes and placenta. The coding region of hPDE-1 was engineered for expression in COS-1 cells, resulting in the overproduction of cAMP PDEase activity. The hPDE-1 recombinant gene product was identified as a low-Km cAMP phosphodiesterase on the basis of several biochemical properties including selective inhibition by the antidepressant drug rolipram. Known inhibitors of other PDEases (cGMP-specific PDEase, cGMP-inhibited PDEase) had little or no effect on the hPDE-1 recombinant gene product. Human genomic Southern blot analysis suggests that this enzyme is likely to be encoded by a single gene. The presence of the enzyme in monocytes may be important for cell function in inflammation. Rolipram sensitivity, coupled with homology to the Drosophila cAMP PDEase, which is required for learning and memory in flies, suggests an additional function for this enzyme in neurobiochemistry.

Cyclic AMP responses are suppressed in mammalian cells expressing the yeast low Km cAMP-phosphodiesterase gene

A genomic DNA fragment from Saccharomyces cerevisiae which contains the SRA5 (=PDE2) gene, coding for a low Km cAMP-phosphodiesterase, was transfected into Chinese hamster ovary cells. Clones carring the cAMP-phosphodiesterase gene were capable of growth in the presence of cholera toxin, which slows the growth of untransfected cells by elevating their cAMP levels. The cholera toxin-resistant transfected cell lines expressed high levels of cAMP-phosphodiesterase mRNA and cAMP-phosphodiesterase activity. Basal intracellular cAMP levels were not significantly affected by the presence of the yeast cAMP-phosphodiesterase gene, but elevation of cAMP levels in response to cholera toxin or prostaglandin E1 was suppressed. Induction of the cAMP-responsive tyrosine aminotransferase promoter by cholera toxin was also blocked in cell lines carrying the yeast cAMP-phosphodiesterase gene. Cholera toxin-resistant transfected cell lines were sensitive to the growth inhibitory effects of N6,02'-dibutyryladenosine 3',5'-monophosphate, which can be used to bypass the effects of the yeast cAMP-phosphodiesterase.

Characterization of the yeast low Km cAMP-phosphodiesterase with cAMP analogues. Applications in mammalian cells that express the yeast PDE2 gene

The essential interactions between cAMP and the yeast low Km cAMP-phosphodiesterase have been analyzed using cAMP analogues and phosphodiesterase inhibitors. cAMP specificity is conferred by hydrogen bonding at the N-6 and N-7 positions. In contrast to the other yeast phosphodiesterase, (Rp)-adenosine 3',5'-monophosphorothioate is not hydrolyzed. Eleven standard phosphodiesterase inhibitors were not highly effective. In Chinese hamster ovary (CHO) cells that express the yeast cAMP-phosphodiesterase (PDE2) gene, cAMP levels cannot be raised by cholera toxin. cAMP analogues that are efficiently hydrolyzed by the yeast cAMP-phosphodiesterase had no effect on the growth of CHO cells that express the PDE2 gene, even though they block the growth and alter the morphology of control cells. cAMP analogues that are not hydrolyzed by the yeast enzyme inhibited the growth and changed the morphology of both control and PDE2 expressing CHO cells. We have developed a method for creating cell lines in which cAMP levels can be reduced by expression of an exogenous cAMP-phosphodiesterase gene. By employing cAMP analogues that are not hydrolyzed by this phosphodiesterase, the inhibitory effects of the enzyme can be bypassed.

Transforming ras proteins accelerate hormone-induced maturation and stimulate cyclic AMP phosphodiesterase in Xenopus oocytes

Transforming Harvey (Ha) ras oncogene products accelerated the time course of Xenopus oocyte maturation induced by insulin, insulinlike growth factor 1, or progesterone. The transforming constructs, [Val-12]Ha p21 and [Val-12, Thr-59]Ha p21, displayed equal potency and efficacy in their abilities to accelerate the growth peptide-induced response. Normal Ha p21 was only 60% as powerful and one-fifth as potent as the mutants containing valine in the 12 position. In contrast, two nontransforming constructs, [Val-12, Ala-35, Leu-36, Thr-59]Ha p21 and [Val-12, Thr-59]Ha(term-174) p21, had no effect on the time course of hormone-induced maturation. Effects of the transforming ras proteins on hormone-induced maturation correlated with their abilities to stimulate in vivo phosphodiesterase activity measured after microinjection of 200 microM cyclic [3H] AMP. When p21 injection followed 90 min of insulin treatment, there was no increase in phosphodiesterase activity over that measured after hormone treatment or p21 injection alone, but additive effects of p21 and insulin on enzyme activity were observed during the first 90 min of insulin treatment. Even though normal Ha p21 and transforming [Val-12, Thr-59]Ha p21 stimulated oocyte phosphodiesterase to equal levels when coinjected with substrate at the initiation of the in vivo assay, the transforming protein elicited a more sustained stimulation of enzyme activity. These results suggest that stimulation of a cyclic AMP phosphodiesterase activity associated with insulin-induced maturation is involved in the growth-promoting actions of ras oncogene products in Xenopus oocytes.

Rescue of the learning defect in dunce, a Drosophila learning mutant, by an allele of rutabaga, a second learning mutant

rutabaga1 (rut1), a Drosophila learning mutant, has adenylate cyclase (EC 4.6.1.1) with reduced basal activity and the absence of calcium/calmodulin-stimulated activity. A second learning mutant, dunce, is defective in cyclic AMP degradation due to decreased or absent phosphodiesterase activity. These opposing biochemical defects allow rut1 to partially suppress the female sterility caused by elevated cyclic AMP levels in dunce flies. Selection of mutations that suppress dunce sterility has led to the isolation of two rutabaga alleles. The alleles (rut2 and rut3) decrease basal adenylate cyclase activity [Bellen, H. J., Gregory, B. K., Olsson, C. L. & Kiger, J. A. (1987) Dev. Biol. 121, 432-444] but, unlike the original rutabaga mutation, leave the calcium/calmodulin-stimulated activity intact. Behaviorally, the two alleles also differ from rut1. One of the mutations partially rescues the dunce learning defect, and flies bearing both alleles learn. Calcium responsiveness may thus be the crucial component of adenylate cyclase activity required for associative learning.

Rat homologs of the Drosophila dunce gene code for cyclic AMP phosphodiesterases sensitive to rolipram and RO 20-1724

The dunce locus of Drosophila melanogaster codes for a low Km, cAMP phosphodiesterase. The correct function of this gene is required for normal learning and memory activity in flies, because dunce mutants fail in tests of behavioral conditioning. These observations have indicated that cAMP regulation is an important aspect of the biochemistry underlying learning and memory processes in insects. To determine whether the locus is functionally conserved in mammals, we have expressed dunce gene homologs from the rat in a yeast expression system. We find that the rat homologs encode low Km, cAMP phosphodiesterases similar to that coded for by the Drosophila dunce+ gene and, more importantly, that the mammalian enzymes are inhibited by rolipram and RO 20-1724, drugs with antidepressant properties. Surprisingly, the dunce-encoded phosphodiesterase was not inhibited by rolipram or RO 20-1724. These findings suggest that the phosphodiesterases, through their regulation of cAMP levels, influence learning and memory in insects and mood in mammals.

The mRNA encoding a high-affinity cAMP phosphodiesterase is regulated by hormones and cAMP

To elucidate the mechanisms by which hormones regulate cAMP phosphodiesterases (PDEs), a group of cDNA clones that had been isolated from a rat Sertoli cell library were characterized. These cDNAs are derived from a single gene (ratPDE3). The deduced amino acid sequence of the ratPDE3 cDNA corresponds to a 66,200-Da protein homologous to other testicular PDEs, to the Drosophila melanogaster dunce-encoded cAMP PDE, and to bovine and yeast PDEs. Expression of ratPDE3 in eukaryotic and prokaryotic cells leads to the appearance of a cAMP PDE with properties identical to the cAMP PDE purified from Sertoli cells. Although of different size, transcripts corresponding to ratPDE3 were present in all organs studied. In the immature Sertoli cell in culture, the level of mRNA transcripts of ratPDE3 was increased more than 100-fold by follicle-stimulating hormone or N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate treatment. Stimulation of ratPDE3 mRNA by N6,O2'-dibutyryladenosine 3',5'-cyclic monophosphate was also observed in a C6 glioma cell line. These data demonstrate that cAMP regulates the expression of one of its own degrading enzymes by an intracellular feedback mechanism that involves changes in mRNA levels.

Molecular cloning of rat homologues of the Drosophila melanogaster dunce cAMP phosphodiesterase: evidence for a family of genes

To study the structure and function of cyclic nucleotide phosphodiesterases (PDEs) involved in mammalian gametogenesis, a rat testis cDNA library was screened at low stringency with a cDNA clone coding for the Drosophila melanogaster dunce-encoded PDE as a probe. This screening resulted in the isolation of two groups of cDNA clones, differing in their nucleotide sequences (ratPDE1 and ratPDE2). In the rat testis, RNA transcripts corresponding to both groups of clones were expressed predominantly in germ cells. Additional screenings of a Sertoli cell cDNA library with a ratPDE2 clone as a probe led to the isolation of two more groups of clones (rat-PDE3 and ratPDE4). Unlike ratPDE1 and ratPDE2, these clones hybridized to transcripts present predominantly in the Sertoli cell. In the middle of the coding region, all four groups of clones were homologous to each other. The deduced amino acid sequences of part of this region were also homologous to the D. melanogaster dunce PDE and to PDEs from bovine and yeast. These data indicate that a family of genes homologous to the D. melanogaster dunce-encoded PDE is present in the rat and that these genes are differentially expressed in somatic and germ cells of the seminiferous tubule. These findings provide a molecular basis for the observed heterogeneity of cAMP PDEs.

Cloning and characterization of mammalian homologs of the Drosophila dunce+ gene

A probe representing the Drosophila dunce+ (dnc+) gene, the structural gene for a cAMP phosphodiesterase (PDEase), detects homologous sequences in many different organisms, including mouse, rat, and human. Genomic and cDNA clones representing a homolog of the Drosophila dnc+ gene were isolated from rat libraries and characterized. This gene has been named ratdnc-1. One cDNA clone defines a large open reading frame of approximately 1.8 kilobases (kb), predicting a protein sequence of 610 amino acids with significant homology to a conserved domain of approximately 275 residues found in most other PDEases. The amino acid identity value to the Drosophila cAMP PDEase within this domain is a striking 75%. Other cDNA clones show blocks of sequence divergence from this cDNA clone close to the predicted N terminus, indicating the potential existence of a family of related enzymes encoded by alternatively spliced messenger RNAs from ratdnc-1. Genomic blotting experiments suggest the existence of at least one other rat gene with homology to ratdnc-1. RNAs homologous to ratdnc-1 are heterogeneous in size between tissues, with heart containing a major transcript of 4.4 kb and brain one of 4.0 kb. The potential identity of the product of the ratdnc-1 gene with known PDEases is discussed.

Isolation and characterization of a mammalian gene encoding a high-affinity cAMP phosphodiesterase

A rat brain cDNA library has been constructed in a Saccharomyces cerevisiae expression vector and used to isolate genes that can function in yeast to suppress the phenotypic effects of RAS2val19, a mutant form of the RAS2 gene analogous to an oncogenic mutant of the human HRAS gene. One cDNA, DPD, was cloned and its genetic and biochemical properties were characterized. A DPD product would share 80% amino acid sequence identity with the Drosophila melanogaster dunce-encoded protein over an extended region. We have shown that the DPD protein is a high-affinity cAMP-specific phosphodiesterase.

Rescue of a Dictyostelium discoideum mutant defective in cyclic nucleotide phosphodiesterase

One of the developmentally induced gene products that is essential for chemotaxis of Dictyostelium amoebae is a cyclic nucleotide phosphodiesterase. The enzyme can be secreted or exist in a membrane bound form. This enzyme is missing in the mutant HPX235 which, as a consequence, does not aggregate unless exogenous cAMP phosphodiesterase is supplied. We have introduced multiple copies of the cloned phosphodiesterase gene into mutant amoebae and restored aggregation. The formation of anatomically correct fruiting bodies, which does not occur when exogenous enzyme is added, is also restored by transformation with the gene. The construct that we have used gives rise only to secreted phosphodiesterase and therefore the membrane bound form of the enzyme is not absolutely required for normal aggregation and morphogenesis.

Disruption of Dictyostelium discoideum morphogenesis by overproduction of cAMP phosphodiesterase

The development and cellular differentiation of Dictyostelium discoideum are disrupted in transformants secreting high levels of the cyclic nucleotide phosphodiesterase. The aggregation of these cells in the early stage of development proceeds rapidly and without the formation of organized streams. The later stages of development, in which differentiation into stalk and spore cells normally takes place, are completely blocked so that the transformants remain in spherical clusters of undifferentiated cells that do not elaborate the tip structure that regulates morphogenesis. These effects are due to overproduction of extracellular phosphodiesterase and demonstrate the role of cAMP during the aggregation phase of development as well as in the control of differentiation and pattern formation.

The cyclic nucleotide phosphodiesterase of Dictyostelium discoideum: the structure of the gene and its regulation and role in development

The cyclic nucleotide phosphodiesterase (phosphodiesterase) of Dictyostelium discoideum plays an essential role in development by hydrolyzing the cAMP used as a chemoattractant by aggregating cells. We have studied the biochemistry of the phosphodiesterase and a functionally related protein, the phosphodiesterase inhibitor protein, and have cloned the cognate genes. A 1.8-kb and a 2.2-kb mRNA are transcribed from the single-phosphodiesterase gene. The 2.2-kb mRNA comprises the majority of the phosphodiesterase mRNA found in differentiating cells and is transcribed only during development from a promoter at least 2.5 kb upstream of the translational start site. The 1.8-kb phosphodiesterase mRNA is detected at all stages of growth and development, is present at lower levels than the developmentally induced mRNA, and is transcribed from a site proximal to the protein-coding region. The phosphodiesterase gene contains a minimum of three exons, and a 2.3-kb intron, the longest yet reported for this organism. We have shown that the pdsA gene and four fgd genes affect the accumulation of the phosphodiesterase mRNAs, and we believe that these loci represent a significant portion of the genes regulating expression of the phosphodiesterase. The phosphodiesterase gene was introduced into cells by transformation and used as a tool to explore the effects of cAMP on the terminal stages of development. In cells expressing high levels of phosphodiesterase activity, final morphogenesis cannot be completed, and differentiated spore and stalk cells do not form. We interpret these results to support the hypothesis that cAMP plays an essential role in organizing cell movements in late development as well as in controlling the aggregation of cells in the initial phase of the developmental program.