Advancing Our Knowledge in Biochemistry, Genetics, and Microbiology Through Studies on Tryptophan Metabolism

Abstract

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. CONTENTS

Ancient Origin of the Tryptophan Operon and the Dynamics of Evolutionary Change

“…The biochemical pathway of Trp biosynthesis is a classical system of biochemical genetics (95,97). In Escherichia coli the component genes are organized into a single transcriptional unit to form the trp operon.…”

“…This system has produced knowledge that extends well beyond the details of the Trp pathway per se, e.g., proof of codon and amino acid VOL. 67, 2003 TRYPTOPHAN OPERON IN PROKARYOTES 307 colinearity and an early precedent for attenuation mechanisms (95,96). The individual reactions of Trp biosynthesis are invariant, but experimental work with a variety of organisms reveals substantial diversity with respect to gene fusion, gene organization, and mechanisms of regulation.…”

“…Regulation of Trp biosynthesis in E. coli, the most widely known system, is quite sophisticated (23,94), being subject to the following multiple levels of control: (i) repression control via the Trp repressor (encoded by the unlinked trpR) which binds Trp as a corepressor moiety, (ii) an attenuation mechanism mediated by a Trp-rich leader peptide (encoded by trpL), and (iii) allosteric feedback inhibition of anthranilate synthase by Trp (95). The E. coli mechanisms of overall trp operon regulation are generally shared by the enteric lineage of Bacteria, defined by us as the clade that includes Shewanella putrefaciens as the outlying point of divergence from E. coli.…”

A Novel Tryptophan Synthase β-Subunit from the HyperthermophileThermotoga maritima

“…In most organisms, the trp genes are organized in operons, which guarantees their coordinated expression in response to the amount of tryptophan available in the growth medium (7). The order of the trp operon from the hyperthermophile Thermotoga maritima trpE(GD)CFBA (8) resembles the organization of the trp operon from Escherichia coli (9).…”

Fifty Years Fused to Lac

“…Recently, he has surveyed the sequenced genome of bacteria, revealing the diversity of pathways in tryptophan biosynthesis and catabolism. Over these many years, he has made particularly important discoveries in mechanisms of gene regulation and the genetic code (56).…”