MODIFICATION OF THE CAPACITY OF BACTERIA TO SYNTHESIZE DEOXYRIBONUCLEIC ACID FOLLOWING X RADIATION: AN IN VIVO AND IN VITRO STUDY

Journal Article · Sat Apr 01 04:00:00 EST 1961 · Pathol. Biol., Semaine Hop.

OSTI ID:4692193

Billen, D

Protein-synthesis inhibition brought about by chloramphenicol (CAP) exposure of Escherichia coli strain 15/sub T-/ subsequently increased the sensitivity of the DNA-synthesizing mechanism to x-ray damage. Whereas the synthesis of DNA was only partially inhibited when log phase cells, exposed to 10000-r x irradiation, were reincubated in a minimal-salts, glucose-thymine medium, the preincubation of the log phase cells with CAP before exposure led to a 100% inhibition of DNA replication by 10000 r. To further substantiate this finding that prior interference with protein synthesis sensitized the DNA- synthesizing mechanism, use was made of a strain of E. coli, strain 15/sub T-/ (555-7), requiring tryptophan, methionine, and arginine in addition to thymine. Protein synthesis was prevented in such cells when they were incubated in an amino acid-free medium, but when reincubated in a complete medium, DNA synthesis resumed at an increasing rate following an initial lag. The resumption of DNA synthesis could be prevented by the addition of CAP to the complete medium. Exposure of the starved cells to 10000 or 20000 r brought about a similar inhibition of resumption of DNA synthesizing activity, in a response almost identical in pattern to that illustrated for untreated E. coli strain 15/sub T-/. Thus, interference with protein synthesis led to the apparent exhaustion of a protein (and possibly RNA) that was necessary for resumption of DNA-synthesizing activity. X-ray exposure or CAP prevented the recovery or replacement of the protein activity. Next a study was undertaken on DNA polymerase and thymidine kinase activity in extracts obtained from cells following the various treatments. Extracts obtained from E. coli strain 15/sub T-/(555-7) exposed to 40000 r were only slightiy less active in incorporating H/sup 3/-thymidine into DNA than control extracts, and exposure of control extract to 40000 r was only partially inhibitory. This indicates that destruction of thymidine-phosphorylating enzymes or DNA polymerase cannot account for the complete suppression of DNA synthesis observed in vivo. In addition, it was shown that pretreatment either by starvation or CAP does not lead to gross depletion of polymerase or thymidine kinase activity although as much as a 50% reduction in H/sup 3/-thymidine incorporation activity was sometimes seen in such extracts. (TCO)

• Research Organization: Univ. of Texas, Houston
• NSA Number: NSA-17-023127
• OSTI ID: 4692193
• Journal Information: Pathol. Biol., Semaine Hop., Journal Name: Pathol. Biol., Semaine Hop. Vol. Vol: 9
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

AMINES
AMINO ACIDS
ANTIBIOTICS
BACTERIA
BIOCHEMISTRY
BIOLOGY AND MEDICINE
CARBOHYDRATES
CHLORAMPHENICOL
DNA
ENZYMES
ESCHERICHIA COLI
LABELLED COMPOUNDS
METABOLISM
NUCLEIC ACIDS
POLYMERASES
PROTEINS
RADIATION DOSES
RADIATION EFFECTS
TRACER TECHNIQUES
TRITIUM
VARIATIONS
X RADIATION