Isolation of a ubiquitin-like (UBL5) gene from a screen identifying highlyexpressed and conserved iris genes

We have screened a human adult iris cDNA library to identify genes that are highly expressed and conserved between humans and pigs. We identified huma n iris cDNAs that hybridized at high stringency to a porcine choroidal ring cDNA probe. Of 1568 human iris cDNAs examined, 176 were found to have high expression in porcine choroidal rings. One of the 176 clones was identifie d as a previously uncharacterized cDNA that we have named the Ubiquitin-lik e 5 gene (UBL5). The UBL5 gene is located on chromosome 19p13.2, and its ge nomic structure has been examined. There is a URL5 pseudogene on chromosome 17p11.2. We have also found homologues to the UBL5 gene in Arabidopsis tha liana, Caenorhabditis elegans, Schizo-saccharomyces pombe, and Saccharomyce s cerevisiae. Northern blot analysis of the Ubiquitin-like gene 5 revealed expression in every tissue tested, with the highest levels of RNA expressio n in heart, skeletal muscle, kidney, liver, iris, and lymphoblasts. Intrace llular localization experiments in COS-7 cells showed that the recombinant UBL5 protein is cytoplasmic. Western analysis demonstrated that the recombi nant UBL5 protein is approximately 9 kDa, as predicted from the cDNA. A com parison between UBL5 and its homologues with other Ubiquitin-like proteins and Ubiquitin, using the PROTDIST program, suggests that the URL5 genes are a separate class of Ubiquitin-like genes. Further characterization of the UBL5 gene will determine the function of the encoded protein and whether it is a candidate for ocular disease. (C) 2001 Academic Press.