The long-range objectives continue to involve the synthesis and testing of compounds related to ribonucleosides, coenzymes, and cofactor analogs, especially those showing specific cell-division and cell-growth activity. During the new grant year, we will concentrate on developing fluorescent, base-specific, site-specific reactions and spray reagents for probing tRNA, viral RNA, other RNA structures, and chromosomes, and for effecting specific modifications including chemical mutations. We will continue the synthesis and test the biological activity and binding of photoaffinity-labeled eukaryotic hormones: cytokinins for plants and 1-substituted adenines that control meiosis in starfish. The goal is to determine the receptors and the spatial and binding requirements at the specific receptor sites. We will synthesize fluorescent photoaffinity-labeled hormones which develop the property of fluorescence emission only upon photolysis and binding. We will develop further our concept of using defined dimensional changes in enzyme substrates and cofactors as a means of demonstrating the geometrical restrictions for their interactions with selected enzymes. The T4-induced RNA ligase enzyme will be used with synthetic nucleoside 3', 5'-diphosphates to incorporate a variety of modified and hypermodified (including fluorescent) nucleosides in oligomers of ordered structure for probing inter-base interactions.