This proposed research project is a continuation of a previous project in which a procedure was developed for constructing a physical map of genes. This procedure involves electron microscopic visualization of ribosome binding sites (translational start sites). Ribosomes are bound to single-stranded DNA, fixed with glutaraldehyde, and the position along the DNA measured. A map constructed for the early and immunity regions of lambda DNA agreed closely with the map determined by other procedures. Further proposed experiments include: 1. mapping of other bacterial virus and plasmid DNA 2. determining if the binding affinity for different binding sites is correlated with the amount of polypeptide product syntesized in vivo. 3. studying translational control in phage T4 4. determining if it is possible to synthesize active enzymes and defined proteins directly from single-stranded DNA 5. to extend this system if possible to eucaryotic viral DNA, chromosomal DNA and mitochondrial DNA.