IDENTIFICATION OF A UBIQUITIN-LIKE PROTEIN IN THE MAMMALIAN VITREOUS-HUMOR

An 8 kDa ubiquitin-like peptide (ULP) was isolated by high performance liquid chromatography from the rabbit vitreous humor, and the N-termi nal amino acid sequence of this peptide showed complete homology with ubiquitin. Western blot revealed the presence of free ULP in both the iris-ciliary (IC) complex and the aqueous humor extracts. In the IC co mplex, fluorescence and immunoelectron microscopy detected high concen trations of ULP in the posterior epithelial cells, suggesting this tis sue as a possible source of ULP in the ocular fluids. Significantly, t his is the first time that the presence of free ULP has been reported in mammalian extracellular fluids. Furthermore, we recently demonstrat ed that the 8 kDa fraction of vitreous humor containing ULP is a poten t inhibitor of protein synthesis [Banerjee et al. (1992): J Cell Bioch em 49:66-73]. These findings taken together suggest a novel biological role for ULP in the control of lens cell growth. (C) 1996 Wiley-Liss, Inc.