This revised proposal requests five years of support for studies assessing the molecular structure and function of the rat testis galactosyl receptor (RTG-r). Studies of RTG-r protein and mRNA suggest that this receptor is related to the rat hepatic lectin 2/3 (RHL-2/3), the minor species of asiologylcoprotein receptor in the liver. The hepatic receptors are responsible for clearing glycoproteins from the circulation after terminal sialic acid residues are removed. Five specific aims are presented. 1) Determine the biochemical and molecular structure of RTG-r, including N- terminus amino acid sequence of peptide fragments, carbohydrate analyses, cDNA isolation and sequencing, and mRNA analysis. In addition, a monospecific, affinity-purified antibody will be prepared against purified RTG-r. 2) Determine the site and mechanism of phosphoylationn of RTG-r. 3) Study the functional role of RTG-r in cell-cell recognition in fetal testis and during spermatogenesis. These experiments will assess the role of RTG-r in specific binding between spermatogenic and Sertoli cells and in mediating the potential migration of fetal germ cells on galactose gradients. 4) Determine whether RTG-r in Sertoli cells occupies a preferential surface domain and is responsible for the receptor-mediated endocytosis of specific ligands. 5) Determine whether RHL-1 (major rat hepatic lectin) affects RTG-r function by introducing functional DNA into Sertoli and spermatogenic cells.