Alternative RNA splicing of the murine alpha A-crystallin gene: protein-coding information within an intron

The eye lens contains a structural protein (alpha-crystallin), composed of two homologous primary gene products, alpha A2 and alpha B2. In certain rodents, there is another minor alpha-crystallin polypeptide, alpha Ains, which is identical to alpha A2 except for a 22 amino acid insert between residues 63 and 64 of the alpha A2 chain. Here we show that the mouse contains a single alpha A-crystallin gene, which has a 1376 bp intron separating codons 63 and 64 of the alpha A2-crystallin mRNA. A sequence encoding a 23 amino acid insert peptide was found 266 bp into the intron. The nucleotide borders of this sequence deviate from the AGGT consensus sequence. The DNA sequence encoding the insert peptide hybridizes to a cytoplasmic 14S RNA, demonstrating that it is transcribed in the lens. We propose that the murine alpha A2-crystallin gene generates both the alpha A2 and the alpha Ains mRNAs by alternative splicing.