CDNA CLONING OF AN ALTERNATIVELY SPLICED ISOFORM OF THE REGULATORY SUBUNIT OF CA2+ CALMODULIN-DEPENDENT PROTEIN PHOSPHATASE (CALCINEURIN B-ALPHA-2)/

A cDNA encoding the regulatory subunit of Ca2+/calmodulin-dependent pr otein phosphatase, calcineurin B (CNB), was isolated from a rat testis cDNA library. It differs from the cDNA obtained from a rat brain cDNA library by an addition of 138 base pairs in the coding region. The co don of the clone from a testis library corresponding to the initiation codon of the clone from a brain library is not ATG but AAG. 5'-noncod ing regions of these cDNAs are also different. The addition in the cod ing region results in the gain of 46 amino acids at the N-terminus. Th ese findings suggest that two distinct isoforms of CNB alpha are deriv ed from the same gene through a process involving alternative utilizat ion of two promoters. We designate the brain type isoform as CNB alpha 1 and the longer isoform as CNB alpha 2. Northern blot analysis and r everse transcriptase-polymerase chain reaction (RT-PCR) followed by So uthern blot analysis suggest that CNB alpha 2 is specifically expresse d in the testis, and its expression is developmentally regulated.