The sequencing of genes corresponding to lens crystallins of higher vertebrates is being actively pursued in a number of laboratories. However, to interdigitate with the rapid advances in the knowledge of crystallin gene structure, it is necessary to develop a cell line capable of synthesizing amounts of crystallin proteins comparable to in situ levels and which is responsive to hormones and other effectors of gene action. Prior attempts to develop crystallin producing cell lines have been only partially successful (e.g. Weinstein et al., 4). Previously described cell lines produce ever diminishing amounts of crystallin proteins in vitro and eventually produce only miniscule amounts of these proteins. Conditional transformation of primary cell lines with temperature-sensitive (ts) oncogenic viruses (e.g. 6) has enabled the cultivation of large amounts of cells that were otherwise intractable to mass culture and which express their differentiated phenotypes. The application of similar techniques to primary bovine lens epithelial cells appears to be scientifically imperative, in order to fully exploit the knowledge rapidly becoming available on the structure of crystallin genes in regard to differentiation and gene action. To achieve the latter end, tsA mutants of SV40 and cloned tsA viral DNA will be used in attempts to develop a differentiated cell line from primary bovine lens epithelial cells. Transformants will be characterized with regard to growth, differentiated characteristics (i.e. lens crystallin content and synthesis) and the regulation of expression of these characteristics.