Title of article :
Mechanism of regulation of transcription initiation by ppGpp. II. Models for positive control based on properties of RNAP mutants and competition for RNAP
Author/Authors :
Melanie M. Barker، نويسنده , , Tamas Gaal، نويسنده , , Richard L. Gourse، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2001
Pages :
14
From page :
689
To page :
702
Abstract :
Strains containing ppGpp, a nucleotide whose synthesis is dependent on the RelA and SpoT proteins of Escherichia coli, display slightly lower rRNA promoter activity and much higher amino acid biosynthesis/transport promoter activity than ΔrelAΔspoT strains. In the accompanying paper, we show that ppGpp directly inhibits rRNA promoter activity in vitro by decreasing the lifetime of the rrn P1 open complex. However, ppGpp does not stimulate amino acid promoter activity in vitro. We show here that RNA polymerase (RNAP) mutants, selected to confer prototrophy to ΔrelAΔspoT strains, mimic the effects of ppGpp on wild-type RNAP. Based on the positions of the mutant residues that confer prototrophy in the structure of core RNAP, we suggest molecular models for how the mutants, and by analogy ppGpp, generally decrease the lifetime of open complexes. We show that amino acid promoters require higher concentrations of RNAP for function in vitro and in vivo than control promoters, and are more sensitive to competition for RNAP in vivo than control promoters. Furthermore, we show that the requirement of an amino acid promoter for ppGpp in vivo can be alleviated by increasing its rate-limiting RNAP-binding step. Our data are consistent with a previously proposed passive model in which ppGpp inhibits stable RNA synthesis directly by reducing the lifetime of the rrn P1 open complex, liberating enough RNAP to stimulate transcription from amino acid promoters. Our data also place considerable constraints on models invoking hypothetical factors that might increase amino acid promoter activity in a ppGpp-dependent fashion.
Keywords :
ppGpp , amino acid biosynthesis , RNA polymerase , stringent response , ribosomal RNA transcription
Journal title :
Journal of Molecular Biology
Serial Year :
2001
Journal title :
Journal of Molecular Biology
Record number :
1240467
Link To Document :
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