It is well documented that the beta-gene of the catalytic (C) subunit of protein kinase A encodes a number of splice variants. These splice variants are equipped with a variable N-terminal end encoded by alternative use of several exons located 5' to exon 2 in the human, bovine and mouse Cbeta gene. In the present study, we demonstrate the expression of six novel human Cbeta mRNAs that lack 99 bp due to loss of exon 4. The novel splice variants, designated CbetaDelta4, were identified in low amounts at the mRNA level in NTera2-N cells. We developed a method to detect CbetaDelta4 mRNAs in various cells and demonstrated that these variants were expressed in human and Rhesus monkey brain. Transient expression and characterization of the CbetaDelta4 variants demonstrated that they are catalytically inactive both in vitro against typical protein kinase A substrates such as kemptide and histone, and in vivo against the cAMP-responsive element binding protein. Furthermore, co-expression of CbetaDelta4 with the regulatory subunit (R) followed by kinase activity assay with increasing concentrations of cAMP and immunoprecipitation with extensive washes with cAMP (1 mm) and immunoblotting demonstrated that the CbetaDelta4 variants associate with both RI and RII in a cAMP-independent fashion. Expression of inactive C subunits which associate irreversibly with R may imply that CbetaDelta4 can modulate local cAMP effects in the brain by permanent association with R subunits even at saturating concentrations of cAMP.