Characterization of murine cDNAs encoding P-57, a neural-specific calmodulin-binding protein

Polyclonal antibodies raised against bovine brain P-57, a neural-specific calmodulin-binding protein, were used to isolate murine cDNAs encoding P-57 from murine brain cDNA libraries in the expression vector lambda gt 11. Two of the overlapping clones contained an open reading frame encoding a polypeptide of 227 amino acid residues (predicted Mr, 23,635), a 163-nucleotide 5'-untranslated sequence, and a 403-nucleotide 3'-untranslated sequence. Hydrophobicity analysis of the predicted polypeptide indicated the lack of any considerable stretch of hydrophobic residues that may span the membrane. This is consistent with prior data suggesting that P-57 exists in a soluble, as well as a membrane-associated, form. The predicted amino acid composition of P-57 is rather unusual in that it is highly enriched in alanine, glutamic acid, and lysine residues, and relatively enriched with proline residues. This amino acid composition accounts for the very low helical content of the predicted polypeptide. A search of the GenBank and EMBL sequence data banks (GenBank Inc., release 44.0 (August, 1986); European Molecular Biology Library, release 8.0 (April, 1986] indicated that the P-57 nucleotide sequence shows no significant homology to any reported sequences. RNA blot analysis of brain, heart, liver, and testes RNA revealed that cDNAs detect P-57 transcripts of 1.5 kilobases in brain, but not in other tissues. Genome blot analysis was consistent with P-57 being encoded by a single or small number of genes. These data demonstrate that the accumulation of this novel calmodulin-binding polypeptide in neural tissue is controlled primarily at the level of RNA abundance.