Biomedical subjects
A Travers
Publications and source records attributed to A Travers.
DNA structure and transcription.
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ppGpp cycle in Escherichia coli.
Kinetics of accumulation and degradation of ppGpp and pppGpp were analysed in spoT+ and spoT strains of Escherichia coli. The experimental data in this paper indicate that on degradation ppGpp is not converted to pppGpp but instead is converted to GDP which is in turn phosphorylated to GTP. In addition the data are consistent with the idea the pppGpp is a direct precursor of ppGpp. We propose that ppGpp is metabolised according to the following pathway: GTP-pppGpp--ppGpp--GDP--GTP, which we call the ppGpp cycle. Coupled with the observations in spot strains we assume that ppGpp blocks its own synthesis by inhibiting the synthesis of pppGpp but not the interconversion of the two nucleotides.
Selective inhibition of tRNATyr transcription by guanosine 3'-diphosphate 5'-diphosphate.
Guanosine 3'-diphosphate 5'-diphosphate (ppGpp) selectively reduces the synthesis of su+III tRNA from omega 80 psu+III DNA relative to the synthesis of omega 80 RNA in a system in vitro containing DNA and Escherichia coli RNA polymerase holoenzyme as the sole macromolecular components. The response of su+III tRNA synthesis to increasing salt and to temperature in the presence of ppGpp suggests that the nucleotide may reduce the affinity of the enzyme for su+III promoters. The Ki for the selective inhibition of tRNA synthesis by ppGpp is 4 muM in contrast to the value of 150 muM for the inhibition of rRNA synthesis.
RNA polymerase specificity and the control of growth.
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Template selection by E. coli RNA polymerase holoenzyme.
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Phage T4 infection restricts rRNA synthesis by E. coli RNA polymerase.
RNA polymerase from T4 infected cells supplemented with E. coli sigma polypeptide has a lower affinity for rRNA promoters than RNA polymerase from uninfected cells. The pattern of transcription by the phage modified polymerase is qualitatively similar to that of the vegetative polymerase in the presence of ppGpp. We suggest that E. coli polymerase holoenzyme normally exists in at least two conformational states, one with a high affinity for rRNA promoters and another with a low affinity, and that T4 infection stabilises the low affinity form.
Modulation of RNA polymerase specificity by ppGpp.
ppGpp alters the initiation specificity of RNA polymerase holoenzyme in vitro in a direction which mimics the stringent response in vivo. The transition temperature for opening rRNA promoters is increased by the nucleotide, that for opening phi80 promoters is unaffected. This implies that RNA polymerase can discriminate between different types of promoter. ppGpp may act by effecting a structural change in the enzyme.
Multiple modes of ribosomal RNA transcription in vitro.
The rate of rRNA synthesis from E. coli DNA in vitro can exhibit an unusual temperature dependence. Instead of the typical sigmoid curve, at least five to six pronounced peaks of rRNA synthesis are detectable over a 30degrees range in temperature. rRNA synthesis from performed initiation complexes exhibits a similar pattern and shows that the number of polymerases able to initiate rRNA synthesis increases with each successive peak. These results are interpreted in terms of a model which proposes that the rRNA cistrons are served by multiple promoter sites (subpromoters) whose activation energies form a graded series. Thus the number of polymerases initiating rRNA synthesis could be controlled by regulating the number of active subpromoters.
Exchange of the sigma subunit of RNA polymerase.
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