Genome-wide analysis of homopolymeric tracts mutation rate in Escherichia coli
Martina, Mariana A. and Barra, José L.
CIQUIBIC–CONICET, Fac. de Ciencias Químicas, UNC
Córdoba, Argentina. E-mail: mamartina@fcq.unc.edu.ar
Generation of genetic diversity through homopolymeric tracts mutation appears to represent a universal system for regulation of gene expression in prokaryotes. We examined the ability of genome context to affect the stability of homopolymeric tracts in Escherichia coli. The stability of a seven-repeat poly-A tract was measured using a reporter gene in which an extra A was introduced changing its reading frame. Isogenic wt and mismatch repair deficient (mutS) E. coli strains with the reporter gene inserted at 23 different locations in the genome were constructed. Rates of frameshift mutations that restore the reporter gene sequence were determined by fluctuation analysis. A difference of up to 13-fold in mutation rate was found among wt strains. If this difference was reflecting a context-dependence of mismatch correction, then it should be lost in mutS cells. However, although mutation rates were elevated in all mutS derivatives, the difference in rate among these strains was still 8.4-fold. This result shows a significant context-dependence of the poly-A stability which is independent of the mismatch correction. We also found that neither the orientation, nor the distance, of the reporter gene relative to the replication origin, nor the density of GATC sites around the poly-A tract have a significant effect on the rate of homopolymeric tract mutation.
Sección: Microbiología molecular
Modalidad de presentación: POSTER
