Studies ard directed toward a better understanding of the role of cyclic nucleotides in the biology of sperm and other reproductive tissues. Major efforts address the matter of cyclic nucleotide binding to receptor/effector proteins in target tissues. The technique of UV-induced direct photoaffinity labeling of these proteins is being evaluated and exploited as an analytical approach. Cyclic nucleotide binding proteins have been identified in messenger ribonucleoprotein particles of testicular cytosol, suggesting a site of control of protein synthesis in this tissue. Cyclic AMP binding in membranes of differentiating slime mold is also being studied. BIBLIOGRAPHIC REFERENCES: Antonoff, R.S., Ferguson, J.J., Jr., & Idelkope, G. Direct Photo-affinity Labeling of Cyclic Nucleotide Binding Proteins with cGMP. Photochemistry and Photobiology 23:327, 1976. Antonoff, R.S. and Ferguson, J.J., Jr. Photoincorporation of 3H-Norepinephrine into a Particulate Preparation from Small Intestine. Fed. Proc. 35:1491, 1976.