Studies of near-ultraviolet radiation induced growth delay in Escherichia coli

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1975

OSTI ID:7282250

Ramabhadran, T V

Sublethal fluences of near-ultraviolet radiation (near uv, 300-380 nm) induce a transient growth inhibition in Escherichia coli. The studies in this dissertation were aimed at elucidating the mechanism of near-uv-induced growth delay in E. coli. Near uv has been shown to induce pyrimidine dimers, alkali-labile bonds, and probably other repairable lesions in DNA. We have shown that growth delay is not photoreactivable and that the extent of growth delay is independent of the dark-repair capacity of the cell, indicating that repairable lesions in DNA are not involved in growth delay. Examination of DNA, RNA, and protein syntheses in near-uv-irradiated E. coli B/r revealed a sharp curtailment of RNA accumulation, the effect on DNA and protein syntheses being milder. The action spectrum for the inhibition of net RNA synthesis suggested the absorption of near uv by 4-thiouridine (/sup 4/Srd), a modified nucleoside in the 8 position of many tRNA's which absorbs in the near uv, to be the cause of inhibition of RNA accumulation. In vitro studies of Favre and others have shown that irradiation of /sup 4/Srd-containing tRNA induces an adduct between this base and a Cytosine at 13 position thereby lowering acylation rate of the tRNA, and incorporation of the corresponding amino acid into polypeptides. /sup 4/Srd is present in 60-65% of E. coli tRNA and about 75% of these tRNA form /sup 4/Srd-Cyd adducts. These considerations led us to suggest that near uv induces an amino acid starvation by decreasing the levels of acylated tRNA and that this leads to the inhibition of RNA accumulation as in ''stringent response''. As observed during an amino acid starvation, the addition of chloramphenicol to near-uv-irradiated cells causes a resumption of RNA accumulation. /sup 4/Srd-Cyd adducts formed in tRNA in vitro by near-uv irradiation have been characterized and the kinetics of its formation have been measured in vitro by Favre and others.

• OSTI ID: 7282250
• Country of Publication: United States
• Language: English

Related Subjects

560131* -- Radiation Effects on Microorganisms-- Basic Studies-- (-1987)
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ANTIBIOTICS
BACTERIA
BIOLOGICAL EFFECTS
BIOLOGICAL RADIATION EFFECTS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
BIOSYNTHESIS
CHLORAMPHENICOL
DNA
DRUGS
ELECTROMAGNETIC RADIATION
ESCHERICHIA COLI
GROWTH
INHIBITION
MICROORGANISMS
NUCLEIC ACIDS
NUCLEOSIDES
NUCLEOTIDES
ORGANIC COMPOUNDS
PHOTOREACTIVATION
PROTEINS
RADIATION EFFECTS
RADIATIONS
REPAIR
RIBOSIDES
RNA
SYNTHESIS
ULTRAVIOLET RADIATION