Abstract
The αA-crystallin protein is the predominant protein in mammalian eye lens. It belongs to the small heat-shock protein family and functions as chaperones for other proteins. Human αA-crystallin is found as various oligomers with a molecular weight between 300 and 1200 kDa, possessing a monomeric molecular weight of 20 kDa. Specific mutations in human αA-crystallin are causative factors for the formation of a common ophthalmological disease called cataract. In this study, we identified an alternatively spliced mRNA transcript (NAC) of human αA-crystallin gene from fetal brain cDNA library. This RNA alternative splicing results in a transcript with an open reading frame of 387 bp. A 49-bp sequence of the tail part of the intron one is spliced as a new head part of the exon two. This ORF encodes a putative protein with 128 amino acid residues. In this encoded protein, the first 63 amino acid residues are conserved with human αA-crystallin and the insertion of the 49-bp segment causes a frameshift with respect to the original αA-crystallin sequence. The frameshift gives rise to a novel 65-residue tail domain. We detected the presence of NAC at the mRNA level by Polymerase Chain Reaction (PCR) and protein level by western blot and no detection of several human tissues and cell lines. We also investigated the characteristics of the structure of NAC protein by Circular Dichroism (CD), 1D Nuclear Magnetic Resonance (NMR) and Dynamic Light Scattering (DLS) experiments. The biological significance of this alternative splicing remains unclear and requires further studies.