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Dominant lethal mutations near the 5' substrate binding site affect RNA polymerase propagation
Ist Teil von
The Journal of biological chemistry, 1993-01, Vol.268 (3), p.2195-2202
Ort / Verlag
Bethesda, MD: American Society for Biochemistry and Molecular Biology
Erscheinungsjahr
1993
Quelle
MEDLINE
Beschreibungen/Notizen
The segment Asp1064-Lys1073 in the beta subunit of Escherichia coli RNA polymerase is evolutionarily conserved and is located
near the "5' face" of the nucleotide binding pocket as was shown by affinity labeling with priming substrates (Grachev, M.
A., Lukhtamov, E. A., Mustaev, A. A., Zaychikov, E. F., Abdukayumov, M. N., Rabinov, I. V., Richter, V. I., Skoblov, Y. S.,
and Chistyakov, P. G. (1989) Eur. J. Biochem. 180, 577-585). We engineered single Xaa-->Ala or Ala-->Ser substitutions of
eight evolutionarily conserved amino acids in this segment as well as a multiple alanine (KRNK) substitution of four of these
residues. The KRNK mutation as well as four of the single substitutions were dominant lethal, two of the single mutations
were recessive lethal, and two were viable. RNA polymerase bearing the dominant mutations was prepared for biochemical study
by in vitro reconstitution from subunits. All of the mutant enzymes formed stable, specific promoter complexes, capable of
initiating RNA synthesis. However, the KRNK polymerase was totally blocked in initiation-to-elongation transition, whereas
the four point mutants displayed allele-specific changes in promoter clearance rate. Each of the four mutations changed, in
a specific way, both the pattern of short oligomers generated in abortive initiation and the pattern of RNA polymerase pausing
during elongation. Thus, the mutations appear to distort but not destroy the active center and to alter, in allele-specific
manner, the coupling between the catalytic reaction and RNA polymerase propagation along the template.