Cyclic AMP Control of Gene Expression in Escherichia coli : the Work of Ira Pastan by

Ira Harry Pastan was born in Winthrop, Massachusetts in 1931. He attended Tufts College where he received his B.S. in 1953 and then went on to Tufts Medical School and earned his M.D. in 1957. After 2 years as an intern and assistant resident at the Yale University School of Medicine’s Grace-New Haven Hospital, Pastan joined the National Institutes of Health (NIH) as a clinical associate in the Clinical Endocrinology Branch. His intention was to pursue a career in clinical medicine or clinical research. At the NIH, Pastan cared for patients with endocrine disorders and studied the mechanism of action of thyroid-stimulating hormone (TSH). He enjoyed research so much that when his 2 years as a clinical associate were over, he decided to pursue a career in basic research. He remained at the NIH and became a postdoctoral fellow with Earl Stadtman, whose work was featured in a previous Journal of Biological Chemistry (JBC) Classic (1). Pastan worked on microbial biochemistry with Stadtman for the next 2 years and then returned to the Clinical Endocrinology Branch in 1963 as a senior investigator to begin his own studies. At first, Pastan went back to working on the mechanism of TSH action. He soon expanded his efforts to include other peptide hormones and cyclic AMP, the second messenger that had just been discovered by Earl Sutherland, as discussed in a previous JBC Classic (2). Pastan started studying the mechanism of action of cyclic AMP using the thyroid gland but decided to switch to Escherichia coli because he thought it would be easier to study the problem in a simpler organism. In the mid-1960s, it was known that glucose repressed inducible enzyme synthesis in E. coli and that cells growing on glucose had low levels of cyclic AMP, whereas starved cells had high cyclic AMP levels. This suggested to Pastan that cyclic AMP might be involved in regulating the synthesis of inducible enzymes. To set about proving this hypothesis, Pastan and his colleagues examined the effects of cyclic AMP on a wide variety of inducible enzymes and transport proteins. This is the subject of the first JBC Classic reprinted here. They found that cyclic AMP overcomes the glucose repression of the synthesis of several inducible enzymes including -galactosidase, galactokinase, glycerokinase, and thymidine phosphorylase. From these results, Pastan concluded, “Since glucose lowers the intracellular concentration of cyclic AMP in E. coli, we propose that the intracellular level of cyclic AMP regulates the rate of THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 282, No. 27, Issue of July 6, p. e21, 2007 © 2007 by The American Society for Biochemistry and Molecular Biology, Inc. Printed in U.S.A.

At the NIH, Pastan cared for patients with endocrine disorders and studied the mechanism of action of thyroid-stimulating hormone (TSH). He enjoyed research so much that when his 2 years as a clinical associate were over, he decided to pursue a career in basic research. He remained at the NIH and became a postdoctoral fellow with Earl Stadtman, whose work was featured in a previous Journal of Biological Chemistry (JBC) Classic (1). Pastan worked on microbial biochemistry with Stadtman for the next 2 years and then returned to the Clinical Endocrinology Branch in 1963 as a senior investigator to begin his own studies.
At first, Pastan went back to working on the mechanism of TSH action. He soon expanded his efforts to include other peptide hormones and cyclic AMP, the second messenger that had just been discovered by Earl Sutherland, as discussed in a previous JBC Classic (2). Pastan started studying the mechanism of action of cyclic AMP using the thyroid gland but decided to switch to Escherichia coli because he thought it would be easier to study the problem in a simpler organism.
In the mid-1960s, it was known that glucose repressed inducible enzyme synthesis in E. coli and that cells growing on glucose had low levels of cyclic AMP, whereas starved cells had high cyclic AMP levels. This suggested to Pastan that cyclic AMP might be involved in regulating the synthesis of inducible enzymes. To set about proving this hypothesis, Pastan and his colleagues examined the effects of cyclic AMP on a wide variety of inducible enzymes and transport proteins. This is the subject of the first JBC Classic reprinted here. They found that cyclic AMP overcomes the glucose repression of the synthesis of several inducible enzymes including ␤-galactosidase, galactokinase, glycerokinase, and thymidine phosphorylase. From these results, Pastan concluded, "Since glucose lowers the intracellular concentration of cyclic AMP in E. coli, we propose that the intracellular level of cyclic AMP regulates the rate of synthesis of many inducible enzymes in E. coli and other microorganisms and that glucose lowers the rate of synthesis of these enzymes by decreasing the intracellular level of cyclic AMP." Following up on these findings, Pastan began to investigate the mechanism by which cyclic AMP and glucose alter the rate of enzyme synthesis. Several groups had suggested that glucose repression was mediated through a reduction in the rate of lac mRNA formation, but no one had been able to directly measure lac messenger levels or synthesis rates during glucose repression. In the second JBC Classic reprinted here, Pastan and his colleagues describe hybridization assays for the measurement of synthesis rates of lac messenger RNA and demonstrate that cyclic AMP and glucose alter the rates of ␤-galactosidase mRNA production.
Pastan eventually discovered that the stimulation of inducible enzyme synthesis requires the interaction of cyclic AMP with a protein he named the cyclic AMP receptor protein (CRP). In the final JBC Classic reprinted here, Pastan and his colleagues describe the purification and properties of this protein.
Pastan later found that cyclic AMP produces an allosteric change in CRP, which increases the affinity of the receptor for DNA sequences in the promoters of many genes. This results in the initiation of transcription and an increase in gene activity. This was the first example of positive control of gene expression. Prior to these studies, the major mechanism of gene regulation was thought to be repression.
In 1970  Pastan has received many awards and honors in recognition of his contributions to science, including the NIH G. Burroughs Mider Lectureship (1973) and the Pierce Immunotoxin Award (1988). He was elected to both the National Academy of Sciences and the American Academy of Arts and Sciences. 1 Harold E. Varmus, Pastan's postdoctoral fellow and coauthor on two of these Classic papers, has also had a very successful career.