OCP1, an F-box protein, co-localizes with OCP2/SKP1 in the cochlear epithelial gap junction region

Immunohistochemical data indicate that OCP1 co-localizes exactly with OCP2 in the epithelial gap junction region of the guinea pig organ of Corti (OC). Despite the abundance of OCP1 in the OC, gaining access to its coding sequence - and, in particular, the 5′ end of the coding sequence - proved unexpectedly challenging. The putative full-length OCP1 cDNA - 1180 nucleotides in length - includes a 67 nucleotide 5′ leader sequence, 300 codons (including initiation and termination signals), and a 216 nucleotide 3′ untranslated region. The cDNA encodes a protein having a predicted molecular weight of 33 700. The inferred amino acid sequence harbors an F-box motif spanning residues 52-91, consistent with a role for OCP1 and OCP2 in the proteasome-mediated degradation of select OC proteins. Although OCP1 displays extensive homology to an F-box protein recently cloned from rat brain (NFB42), clustered sequence non-identities indicate that the two proteins are transcribed from distinct genes. The presumptive human OCP1 gene was identified in the human genome databank. Located on chromosome 1p35, the inferred translation product exhibits 94% identity with the guinea pig OCP1 coding sequence.