Identification and expression of mrna for lensspecihccalpain: Lp74

Using RT-PC'R. we reported here the identification or a splice mutant form of muscle-specific ealpain (p94) from the lens of eyes of rat designated "Lp74". mRNA for Lp74 was found to be transcribed nnly in lens, and no other tissues assayed by RT-PCR analysis showed significant I,p74 mRNA. Amounts of the Lp74 mRNA in rat lens "-en- found abundantly and almost equal to those for m-calpain, ihe predominant form of ubiquitous ealpain in lens. The cDNA of I.p74 ;,s identical to rat muscle p94. except for three major deletions. Deletions of most of the nudeotides from exon 1, and exiiLt deletions of exon ft. 15 and 16 resulted in a deduced Lp74 protein lacking most of NS region, and much of IS I and 1S2 regions unique to ps>4 The predicted catalytic subunit of 74 kDa protein ould contain the usual active site residues for a cysteine protease as in other ealpain large subunits as well as a calcium binding domain. Although the expression of I.p74 protein from lens material still needs 10 he performed, these findings may providé insight into a lensspec, tfii. function, related to the unique physiology and biochemistry of lens, .is well .is helping to define the roles of NS. IS1 and 1S2 regions ;n muscle pn4.