During entry into stationary phase, Escherichia coli expresses many genes which
impart cellular resistance to numerous environmental stresses such as oxidative or acid
stress. Many ofthese genes are regulated by the alternative sigma factor, RpoS To
identify additional genes regulated by RpoS, a phenotype independent genetic screen was
previously employed (L. Wei Masters thesis). The identities ofthe ten most highly RpoSdependent fusions were determined by DNA sequencing and subsequent sequence analysis
using the BLAST algorithm Three fusions map to genes previously known to be RpoSdependent while the remaining seven represent new members ofthe regulon The
expression of many ofthe RpoS-dependent fusions remained growth phase dependent
even in the rpoS background This suggests that other growth phase regulatory factors in
addition to RpoS may coordinate stationary phase gene expression Upon sequencing the
remaining rsd fusions, three mutants mapped to narY which is part ofthe narZYWV
operon encoding the secondary nitrate reductase Z (NRZ) This operon was selected for
further investigation since NRZ has been previously reported to be constitutively
expressed Expression studies using promoter lacZ fusions and nitrate reductase assays
reveal that NRZ is induced ten-fold at the onset ofstationary phase and twenty-fold in the
presence of nitrate Like other rsd fusions, growth phase dependent expression was
observed in an rpoS background indicating that other regulatory factors may be involvedn the regulation of NRZ Northern analyses using probes specific to NRZ confirmed that
transcription of NRZ is indeed dependent on RpoS. These results suggest that RpoS
mediated regulation of NRZ may be an important physiological adaptation to reduced
oxygen levels during transition to stationary phase / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29587 |
| Date | 12 1900 |
| Creators | Chang, Lily |
| Contributors | Schellhorn, H.E., Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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