Rapid enhancement of "MIP" 26kDa protein phosphorylation by RF-36 nucleic acid binding protein in lens cells.

Previous work from this laboratory has suggested that a lens regulatory protein, RF-36, possesses pleiotropic function in a homeotic switch during lens growth and differentiation. Evidence for this was derived from its interaction with specific receptors on the cell surface. Within minutes after incubation in lens cell culture system, enhanced membrane protein phosphorylation occurred. This process apparently activated at least two kinase-like activities, e.g. General kinase C and tyrosine kinase. The molecular weight of the phosphorylated protein was found to be 26kDa. Immunological studies indicated that the 26kDa component is part of the so-called "MIP" intrinsic membrane protein. Compared with other oncogenic proteins, there are no structural similarities between RF-36 and oncogenes. These data strongly suggest that RF-36 has a major pleiotropic function as a special kind of informational molecule; that is, a chemical messenger in promoting signal transduction in lens tissue.