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  • RNA polymerase  (1)
  • 1
    ISSN: 1617-4623
    Keywords: Stringent control ; RNA polymerase ; Escherichia coli
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Previous studies on two Escherichia coli rpoB mutants, carrying single amino acid substitutions at approximate amino acid positions 736 and 906 in the β subunit, showed that these alterations in the RNA polymerase resulted in an apparent reduced response to valine-induced amino acid starvation in vivo and prevented ppGpp-mediated inhibition of transcriptional initiation at stable RNA promoters in vitro. These observations suggested that the mutations had altered either the ppGpp binding site or the promoter selectivity of the enzyme. The in vivo analysis presented here indicates that these mutants encode an RNA polymerase that responds normally to changes in the level of ppGpp; their apparent relaxedness is due to a reduced accumulation of ppGpp during isoleucine starvation. Thus, there is no indication that the mutations have altered ppGpp binding sites. These observations and the difference between in vitro and in vivo results can be explained by the assumption that the mutations produce an extended ppGpp-dependent pausing of RNA polymerase during the transcription of unstable RNA. Comparison of the vivo and in vitro effects of ppGpp on rrn transcription further suggests that these reflect different phenomena, although in both cases ppGpp inhibits rrn transcription.
    Type of Medium: Electronic Resource
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