I knew Nick for nearly four decades. In the 1960s, tremendous progress was being made in the study of enzymes that replicate DNA. After receiving his PhD in 1966, Nick decided to join Arthur Kornberg's laboratory at Stanford University, a Mecca in the world of DNA enzymology. It was there that I first met him. I was at that time measuring the extent of supercoiling of Escherichia coli plasmids of different sizes, hoping that such data might provide a clue as to why DNA rings purified from cells were supercoiled. After hearing a talk I gave at Stanford, Nick came up and offered me a sample of an E. coli plasmid that he had just discovered, which, with a contour length of a little under 2 μm, was the smallest DNA ring known at that time. The small size and low copy number per cell made it difficult to obtain enough of the plasmid for quantitative measurements; a few days later, however, Nick showed up in my office at Berkeley, with an ice bucket containing a generous sample of the precious DNA. Nick's enthusiasm for science, and his generosity with his time, material and research findings, would remain unchanged over the decades I knew him.

Nick joined the faculty of the University of Chicago in 1968. Because studies on DNA replication in most of the leading centers then were sharply focused on the E. coli system, Nick chose to concentrate his own efforts on the DNA polymerases of the Gram-positive bacterium Bacillus subtilis, which is far removed from the Gram-negative E. coli. One of his early projects was a study of the compound 6-(p-hydroxyphenylazo)-uracil, an inhibitor of DNA synthesis in B. subtilis but not in E. coli. He and his associates soon deduced that the target of this compound is DNA polymerase III and that inhibition involves the formation of a ternary complex consisting of the antimicrobial agent, the polymerase and the DNA template at a position where a C awaits the incorporation of a dGTP.

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