Relative orientation of gene, messenger and polypeptide chain

Advancing our knowledge in biochemistry, genetics, and microbiology through studies on tryptophan metabolism

I was fortunate to practice science during the last half of the previous century, when many basic biological and biochemical concepts could be experimentally addressed for the first time. My introduction to research involved isolating and identifying intermediates in the niacin biosynthetic pathway. These studies were followed by investigations focused on determining the properties of genes and enzymes essential to metabolism and examining how they were alterable by mutation. The most challenging problem I initially attacked was establishing the colinear relationship between gene and protein. Subsequent research emphasized identification and characterization of regulatory mechanisms that microorganisms use to control gene expression. An elaborate regulatory strategy, transcription attenuation, was discovered that is often based on selection between alternative RNA structures. Throughout my career I enjoyed the excitement of solving basic scientific problems. Most rewarding, however, was the feeling that I was helping young scientists experience the pleasure of performing creative research.

Rapid mapping of conditional and auxotrophic mutations in Escherichia coli K-12

The approximate genetic map locations of auxotrophic and conditional lethal mutations of Escherichia coli can be rapidly determined with replica plating techniques. A set of patches of 15 streptomycin-sensitive (Str(S)) Hfr strains with points of origin distributed around the map is replica plated onto a recombinant-selective plate with a lawn of Str(R) cells which carry an unmapped mutation. The map interval defined by the Hfr points of origin which are closest to the mutant locus is seen by the presence or absence of heavy patches of recombinants produced by transfer of early wild-type genes from the Hfrs. An alternative method is to replicate patches of different mutant strains (100 per plate) onto Hfr lawns; in this case more than 1,000 different mutants can be mapped in a single experiment in a few days. In this way, many types of mutations with similar phenotypes can be grouped as to approximate location on the genetic map. For ordering mutations within groups, the same replica plating methods can be used to cross F-prime derivatives of mutants with other mutants of the same group. Relative merits of these and other mapping methods of E. coli are discussed.

Direction of translation in bacteriophage S13

Suppressible (amber-type) mutants in gene IIIa of bacteriophage S13 show polarity in reducing the activity of only the neighboring gene IIIb. The polarity implies that the genome is translated in the direction of IIIa to IIIb. From the known homology of the messenger RNA with the single-stranded DNA, the orientation of the DNA with respect to the genetic map can also be inferred.

Orientation of nonsense codons on the genetic map of the lac operon

Intracodon recombination is used to orient the nonsense codons UGA, UAG, and UAA on the genetic map of the (lactose) lac operon of Escherichia coli. The 5'-end of these triplets is toward the operator end of the operon. A hypothesis is presented to explain the fact that the frequency of recombination between adjacent nucleotides is many times lower than expected.