Biomaterial Database

Temperature-dependent mutational specificity of an Escherichia coli mutator, dnaQ49, defective in 3'----5' exonuclease (proofreading) activity. 1989

R J Isbell, and R G Fowler

Department of Biological Sciences, San Jose State University, CA 95192.

Escherichia coli strains carrying the temperature-dependent dnaQ49 allele are strong mutators at 37 degrees C. Since the dnaQ49 gene encodes the epsilon subunit of DNA polymerase III, it is thought that the large number of errors results in part from impaired proofreading activity during DNA replication. We have examined dnaQ49-induced reversion patterns of defined trpA alleles to determine the kinds of errors produced by dnaQ49 at 30 degrees C and 37 degrees C. We found that at 37 degrees C dnaQ49 produced all types of base-pair substitutions in addition to frameshifts with transitions generally occurring more frequently than transversions. This generalized mutator activity is very similar to that displayed in rich medium by mutD5, another mutator allele at the dnaQ locus. However, when dnaQ49 strains were cultured at 30 degrees C, not only were reversion frequencies much lower than at 37 degrees C, but in addition, the spectrum was altered. Transversions became proportionally more prevalent in the reversion spectra at the lower temperature. We suggest the possibility that at 37 degrees C dnaQ49 results in defective proofreading and methyl-directed postreplicative mismatch repair, while at 30 degrees C mismatch repair is fully and proofreading partially restored.

UI	MeSH Term	Description	Entries
D009154	Mutation	Any detectable and heritable change in the genetic material that causes a change in the GENOTYPE and which is transmitted to daughter cells and to succeeding generations.	Mutations
D004926	Escherichia coli	A species of gram-negative, facultatively anaerobic, rod-shaped bacteria (GRAM-NEGATIVE FACULTATIVELY ANAEROBIC RODS) commonly found in the lower part of the intestine of warm-blooded animals. It is usually nonpathogenic, but some strains are known to produce DIARRHEA and pyogenic infections. Pathogenic strains (virotypes) are classified by their specific pathogenic mechanisms such as toxins (ENTEROTOXIGENIC ESCHERICHIA COLI), etc.	Alkalescens-Dispar Group,Bacillus coli,Bacterium coli,Bacterium coli commune,Diffusely Adherent Escherichia coli,E coli,EAggEC,Enteroaggregative Escherichia coli,Enterococcus coli,Diffusely Adherent E. coli,Enteroaggregative E. coli,Enteroinvasive E. coli,Enteroinvasive Escherichia coli
D005092	Exonucleases	Enzymes that catalyze the release of mononucleotides by the hydrolysis of the terminal bond of deoxyribonucleotide or ribonucleotide chains.	Exonuclease,3'-5'-Exonuclease,3'-5'-Exonucleases,5'-3'-Exonuclease,5'-3'-Exonucleases,3' 5' Exonuclease,3' 5' Exonucleases,5' 3' Exonuclease,5' 3' Exonucleases
D000483	Alleles	Variant forms of the same gene, occupying the same locus on homologous CHROMOSOMES, and governing the variants in production of the same gene product.	Allelomorphs,Allele,Allelomorph
D001482	Base Composition	The relative amounts of the PURINES and PYRIMIDINES in a nucleic acid.	Base Ratio,G+C Composition,Guanine + Cytosine Composition,G+C Content,GC Composition,GC Content,Guanine + Cytosine Content,Base Compositions,Base Ratios,Composition, Base,Composition, G+C,Composition, GC,Compositions, Base,Compositions, G+C,Compositions, GC,Content, G+C,Content, GC,Contents, G+C,Contents, GC,G+C Compositions,G+C Contents,GC Compositions,GC Contents,Ratio, Base,Ratios, Base
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures