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J Bacteriol. 1969 July; 99(1): 91-100
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Fidelity of Initiation of Protein Synthesis After Premature Chain Termination in Polarity Mutants¹

^a Department of Microbiology and Immunology, Duke University School of Medicine, Durham, North Carolina 27706

ABSTRACT

ß-Isopropylmalate dehydrogenase, the product of the second cistron of the leucine operon in Salmonella typhimurium, produced by strains bearing nonsense or frameshift mutations in the first cistron of the operon was shown to be homogeneous as judged by electrophoretic and immunological techniques. Amino terminal analyses suggest that the enzyme produced by the mutant strains is identical with the wild-type enzyme. This view is supported by the observation that a nonsense mutant strain ß-isopropylmalate dehydrogenase copurifies with the wild-type enzyme. The results suggest that the uncoupling of normal chain termination and reinitiation does not interfere with the fidelity of subsequent polypeptide chain initiation in a polycistronic messenger ribonucleic acid.

² Microbiology trainee, National Institutes of Health Training Grant GM 1019.

¹ This work was submitted by the first author in partial fulfillment of the requirements for the Ph.D. degree in the Department of Microbiology and Immunology in the Graduate School of Arts and Sciences of Duke University.