Molecular cloning of a tissue-specific protein kinase (C gamma) from human testis--representing a third isoform for the catalytic subunit of cAMP-dependent protein kinase.
Two different mammalian genes for the catalytic subunit (C) of cAMP-dependent protein kinase have previously been characterized (C alpha, C beta). In the present study, we report the molecular cloning of a third isoform of C, from a human testis cDNA library, as well as the isolation of human cDNAs for C alpha and C beta. This third form of C, which we will designate C gamma, is clearly derived from a distinct gene and shows a tissue-specific expression. A close evolutionary relation between C gamma and C alpha was suggested by nucleotide homologies (86% inside the open reading frame, 81% in the 3'-untranslated region). Thus, the C gamma cDNA cross-hybridized with the 2.8 kilobase (kb) C alpha mRNA, present at high levels in most human tissues, as well as with a 1.8 kb C gamma-specific mRNA, which was only found at detectable levels in human testis. However, at the amino acid level, C alpha and C beta showed a close relationship (93% homology), whereas C gamma diverged significantly from both C alpha (83%) and C beta (79%). Taken together with the tissue-specific expression of C gamma, this suggests a pressure on C gamma during evolution, acting to modulate it in a functionally specific way. Certain amino acid substitutions make C gamma a distinct member of the cAMP-dependent subfamily of protein kinases, and suggest that C gamma may be distinct in its protein substrate specificity or its interaction with the different regulatory subunits.
Beebe
S J
SJ
Institute of Pathology, Rikshospitalet, Oslo, Norway.
Oyen
O
O
Sandberg
M
M
Frøysa
A
A
Hansson
V
V
Jahnsen
T
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics*; D011493:Protein Kinase C / Q000235:genetics* / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D015183:Restriction Mapping; D013737:Testis / Q000201:enzymology*
D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D012333:RNA, Messenger; C015482:protein kinase modulator; D004247:DNA; D011494:Protein Kinases; D011493:Protein Kinase C