Rat RIβ isoform of type I regulatory subunit of cyclic adenosine monophosphate‐dependent protein kinase: cDNA sequence analysis, mRNA tissue specificity, and rat/mouse difference in expression in testis

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Abstract
A rat complementary DNA (cDNA) for the RIβ isoform of type I cyclic adenosine monophosphate (cAMP)‐dependent protein kinase regulatory subunit was cloned and sequenced and was found to contain the entire protein coding and 3′‐untranslated regions, with a single (ATTAAA) poly‐adenylation site. The largest open reading frame was preceded by a short outof‐phase open reading frame, which is not seen in the corresponding mouse RIβ cDNA due to a single base substitution. The rat RIβ cDNA clone was 2,374 bases long and detected a rat mRNA of approximately 2.8 kilobases. Rat RIβ mRNA was abundant in adult rat brain and testis but was undetectable in other rat tissues. The rat RIβ cDNA also detected RIβ mRNA in mouse brain, but not mouse testis, from 10‐week‐old BALB/c or 10‐ and 6‐week‐old Swiss Webster mice. Thus, despite a 96% nucleotide identity in the coding region of RIβ in rat vs. mouse, there are at least two differences in these closely related species. First, there is a short open reading frame, which precedes the coding region in the rat but not the mouse. Second, unlike the mouse testis, the rat testis contains abundant levels of RIβ mRNA.