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J. Biol. Chem., Vol. 277, Issue 48, 46319-46327, November 29, 2002

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DNA Polymerase III from Escherichia coli Cells Expressing mutA Mistranslator tRNA Is Error-prone^*

Abu Amar M. Al Mamun, Kenneth J. Marians^§, and M. Zafri Humayun^¶

From the  University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Department of Microbiology and Molecular Genetics, International Center for Public Health, Newark, New Jersey 07101-1709 and ^§ Molecular Biology Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021

Translational stress-induced mutagenesis (TSM) refers to the elevated mutagenesis observed in Escherichia coli cells in which mistranslation has been increased as a result of mutations in tRNA genes (such as mutA) or by exposure to streptomycin. TSM does not require lexA-regulated SOS functions but is suppressed in cells defective for homologous recombination genes. Crude cell-free extracts from TSM-induced E. coli strains express an error-prone DNA polymerase. To determine whether DNA polymerase III is involved in the TSM phenotype, we first asked if the phenotype is expressed in cells defective for all four of the non-replicative DNA polymerases, namely polymerase I, II, IV, and V. By using a colony papillation assay based on the reversion of a lacZ mutant, we show that the TSM phenotype is expressed in such cells. Second, we asked if pol III from TSM-induced cells is error-prone. By purifying DNA polymerase III* from TSM-induced and control cells, and by testing its fidelity on templates bearing 3,N⁴-ethenocytosine (a mutagenic DNA lesion), as well as on undamaged DNA templates, we show here that polymerase III* purified from mutA cells is error-prone as compared with that from control cells. These findings suggest that DNA polymerase III is modified in TSM-induced cells.

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