By antibody screening of a rat liver and a rat heart cDNA library in lambda gt11 two clones coding for the liver‐ and heart‐specific subunit VIa of rat cytochrome c oxidase were isolated. In the heart cDNA sequence a TAA stop codon was found in frame 18 bp 5′ upstream of the first methionine codon, thus excluding a leader sequence for this protein. The two cDNAs contain the full‐length coding region of two subunits. The amino acid sequences of the two subunits show only 50% homology, whereas 74% homology was found between rat heart and bovine heart subunit VIa. By Northern blot analysis it is shown that the gene for subunit VIa from heart is only expressed in heart and skeletal muscle, whereas that from liver is also expressed in kidney, brain, heart and weakly in muscle.

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A cDNA of a novel form of type V adenylyl cyclase has been cloned from rabtut myocardmm using ohgonucleotlde probes denved from peptides that were produced by enzymatic cleavage of punfied heart cyclase A correspondmg mRNA (6 kb) has been detected m rabtnt myocarchal tissue by Northern blot analysis The cDNA encodes a protein of 1,264 ammo acids exhlbltmg 12 putatwe membrane-spanning regons m its hydroplnhclty profile Sequence comparison to two other previously published type V adenylyl cyclases reveals ammo-terminal domams of different length and low correlative homology, whereas the rest of the sequences IS almost identical The nonconserved ammo-terminal region of the subtype consists of 214 ammo acids and exceeds the length of the others by 40 and 80 residues, respectively Its presence m membrane preparations from different tissues has been confirmed immunologically usmg an antibody directed against a synthetic peptide The cloned adenylyl cyclase was functionally expressed m COS-1 cells to attam an enzymatrc actlvlty 3 S-to 1Cfold above control m the presence of forskohn

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