Structural and functional characterization of the exonuclease I (sbcB) gene and gene product from Escherichia coli and a Markov chain analysis of DNA sequences

Thesis/Dissertation · Thu Jan 01 04:00:00 EST 1987

OSTI ID:5233413

Phillips, G J

The nucleotide sequence for the structural gene for exonuclease I (sbcB) from Escherichia coli was determined. Two putative promotes for this gene were identified and were predicted to have weak transcription initiation activity. In addition, the sbcB coding region contains many non-optimal codons. These observations are consistent with the suggestions that sbcB is a poorly expressed gene. Several mutant exonuclease I genes were cloned onto pBR322 plasmids. These genes represented both sbcB and xonA mutation. One of the xonA mutation (xonA6) was associated with a 1.2-kb insertion of an IS-30 related mobile genetic element in the 3'-region of the gene. Two of the mutations (xonA2 and xonA6) encode unstable polypeptides. Determination of exonucleolytic activity on single-stranded DNA from cell extracts containing each of the cloned mutant genes revealed no correlation between residual exonucleolytic activity and the pheno-types of sbcB and xonA mutants. A proposal that the exonuclease I protein contains an additional activity besides its ability to degrade single-stranded DNA is presented. Characterization of E. coli strains which overproduce exonuclease I showed increased sensitivity to UV irradiation.

• Research Organization: Georgia Univ., Athens (USA)
• OSTI ID: 5233413
• Country of Publication: United States
• Language: English

Related Subjects

560130* -- Radiation Effects on Microorganisms
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
BACTERIA
CLONING
DNA SEQUENCING
DNA-CLONING
ELECTROMAGNETIC RADIATION
ENZYME ACTIVITY
ENZYMES
ESCHERICHIA COLI
ESTERASES
GENE MUTATIONS
GENES
HYDROLASES
MICROORGANISMS
MUTANTS
MUTATIONS
NUCLEASES
PHENOTYPE
PHOSPHODIESTERASES
RADIATIONS
RADIOSENSITIVITY
STRUCTURAL CHEMICAL ANALYSIS
TRANSCRIPTION
ULTRAVIOLET RADIATION