Isolation of a cDNA encoding a glutathione S-transferase (GST) class-pi from the bovine ocular ciliary epithelium

We have used a polyclonal antiserum to bovine ciliary epithelium, a secretory tissue involved in the formation of aqueous humor, to immunoscreen a directional lambda gt11 Sfi-Not cDNA expression library prepared from bovine ciliary epithelium poly(A)+ RNA. After immunoscreening 6 x 10(5) independent clones, 41 cDNA clones positive for ciliary epithelium were isolated and characterized. About one-third of the positive cDNA clones were found to be identical and to encode a glutathione S-transferase (GST) class-pi. The largest bovine GST cDNA clone isolated, pCN11, contains an open reading frame of 630 bases, encoding a protein of 210 amino acids with a calculated molecular weight of 23,335 Da. The corresponding amino acid sequence showed an overall identity of 85.6% with the human, and 85.2% with the rat and mouse GST class-pi. Northern analysis of bovine ocular tissues revealed that the GST class-pi gene encodes a 0.8-kilobase mRNA which is expressed most abundantly in cornea, ciliary epithelium and retina, and in lower levels in iris and lens. Cell lines derived from non-pigmented or pigmented bovine ciliary epithelium also showed high levels of GST-pi mRNA expression. These results provide additional evidence for differential gene expression of GST class-pi mRNA in various areas of the bovine eye.