ARPP-21, a cyclic AMP-regulated phosphoprotein enriched in dopamine-innervated brain regions. II. Molecular cloning...

A cDNA clone for the mRNA of bovine ARPP-21 (cAMP-regulated phosphoprotein, Mr = 21,000 as determined by SDS-PAGE) was isolated from a modified Okayama-Berg plasmid library. Transformed Escherichia coli colonies were screened by in situ colony hybridization with 2 different oligonucleotide probes derived from the amino acid sequence of the bovine protein. Sequence analysis of the longest cDNA clone, pTKAI [2407 nucleotides plus a poly(A) tail], revealed a 267-nucleotide-long coding region in agreement with the bovine ARPP-21 amino acid sequence (Williams et al., 1989). Southern blot analysis of total bovine genomic DNA raised the possibility that there may be 2 genes coding for ARPP-21. Northern blot analysis of total cellular RNA from bovine caudate nucleus and other brain regions demonstrated the existence of 2 major mRNA species, 2.5 and 1.0 kb in length, probably derived from use of alternate polyadenylation sites. There was a differential expression of these 2 mRNAs within the brain. Both ARPP-21 mRNAs were most abundant in the caudate nucleus, where the concentration of the protein is highly enriched.