LENS EPITHELIAL-CELL MESSENGER-RNA .1. CLONING AND SEQUENCING OF A MESSENGER-RNA WITH A BASIC MOTIF LEUCINE-RICH DOMAIN SPECIFICALLY EXPRESSED IN RAT LENS EPITHELIAL-CELLS

By methods of subtraction-hybridization of lambda ZAP cDNA libraries, prepared from 4-week-old rat lens epithelial cells (capsule) and lens fiber cells (decapsulated lens), we have isolated a specific cDNA clon e whose target mRNA is about 600 b long. Northern blot hybridization a nalysis data showed that the target mRNA was preferentially expressed in the lens epithelial cells; it was not found in the retina or in non -ocular tissues. The complete sequence of the mRNA was obtained both b y the 5' and 3' rapid amplification of cDNA ends (5'-RACE, 3'-RACE), a nd by sequencing of a clone containing the full-length cDNA insert. It contains 599 b, with an open reading frame at nucleotide (nt) 30 (ORF (30)). The base sequence appears to represent a complete sequence of t he target mRNA, with a poly(A) signal at nt 563-569, and a poly(A) tai l at nt 582 (GenBank accession #U15149). In situ hybridization showed that the target mRNA was localized in the anterior epithelial cells, a nd in the elongating cells in the bow region. The encoded protein of 5 7 amino acids (aa) contains a basic and an acidic domain. It is rich i n leucine, which is located at the basic region of the ORF at every fo urth aa, and at the acidic region at eight aa intervals. Therefore, th ere is a periodicity in the appearance of leucine residues in the dedu ced primary sequence, as has been seen in DNA binding proteins. Search of GenBank, EMBL and Swiss-Prot did not yield significant homology to any of the entered sequences in those databanks. Our data demonstrate that we have isolated a cDNA clone containing novel sequences specifi cally expressed in lens epithelial cells.