(A) Schematic diagram of human PDE4A mRNA transcripts and their encoded proteins. The five dark stippled boxes indicate the unique N-terminal regions of the proteins encoded by the following cDNAs: PDE4A1 (GenBank® accession number U97584 [17]); PDE4A4 (GenBank® accession number L20965 [10]); PDE4A8 (GenBank® accession number AY593872; the present study); PDE4A10 (GenBank® accession number AF178570 [14]); PDE4A11 (GenBank® accession number AY618547 [15]). Also shown are regions of sequences that are highly conserved in other PDE4 isoforms, including the common long region, UCR1, UCR2 and the catalytic region. UCR1, UCR2 and the catalytic region are in turn separated by less conserved sequence regions, called LR (linker region) 1 and LR2. The C-terminal region is unique to PDE4A isoforms. The PKA phosphorylation site common to all long PDE4 isoforms is also indicated. (B) Alignment of the amino acid sequences of the N-terminal regions of the five human PDE4A proteins, as deduced from their cDNAs. Underlined regions indicate UCR1 and UCR2. Only the first 300 amino acids of the alignment are shown, as the remaining sequences of the four isoforms are all identical, as we and others have described previously [5]. (C) Alignment of the unique 5′-region of the human PDE4A8 cDNA with its corresponding genomic sequence (Genom; part of GenBank® accession number AC011548.4). Capital letters indicate regions of sequence identity. Dots indicate the 5′- and 3′-ends of exons. The physiological start codon is indicated in bold type. (D) Alignment of the nucleotide sequences of the unique 5′-regions of the human and rat PDE4A8 cDNAs. Vertical lines indicate sequence identities. Dots indicate gaps inserted by the program to improve the alignments. The physiological start codons and upstream in-frame stop codons are indicated in bold type. Also shown is the rat PDE4A8 amino acid sequence (GenBank® accession number L36467 [13]).