Sedimentation of DNA of Dictyostelium discoideum lysed on alkaline sucrose gradients. Role of single-strand breaks in gamma ray lethality of sensitive and resistant strains

Journal Article · Sat Sep 15 00:00:00 EDT 1973 · J. Mol. Biol., v. 79, no. 2, pp. 267-284

DOI:https://doi.org/10.1016/0022-2836(73)90005-3· OSTI ID:4438106

Khoury, A T; Deering, R A

The nuclear and mitochondrial DNA of the amoebae of the cellular slime mold Dictyostelium discoideum were labeled with (methyl-/sup 3/H! thymidine by allowing them to grow on Escherichia coli 15T- containing this label in its DNA. Neutral CsCl gradients were used to identify the labeled molecules. Alkaline sucrose sedimentation profiles of cells lysed directly on the gradients revealed two high molecular weight species, one of about 90 S (single-strand mol wt = 1.4 x 10/sup 8/) identified by alkaline CsCl rebanding as nuclear DNA, and another of 43 S (single-strand mol wt = 2.3 x 10/sup 7/), identified as mitochondrial DNA. These gradients were used to study the production of single-strand breaks and their rejoining in DNA of a gamma-resistant strain (NC-4; 10% survival dose for cell proliferation, D/sub 10/ = 75 krad) and in two radiation-sensitive daughter mutants (ys-18, D/sub 10/= 75 krad; ys-13, D/sub 10/ = 4 krad). With /sup 60/Co gamma rays, breaks were produced in nuclear and mitochondrial DNA at an efficiency of one break per 33 eV in all three strains. At doses up to about 100 krad, these single-strand breaks were closed equally well during post-irradiation incubation of NC-4, ys-18, and ys-13, even though their survlvals were widely different, indicating no apparent correlation between parental strand rejoining and survival in the sensitive strains. At higher doses, post-irradiation treatment with 1 mg caffeine/ml sensitized NC-4 and retarded strand-rejoining, suggesting that lethality in this resistant strain may be related to strand breaks. Single-strand rejoining is considered a necessary, but not sufficient, condition for radiation survival in this organism. The nature of the apparently unrepaired lesions leading to lethality in the sensitive strains was not known. (auth)

• Research Organization: Pennsylvania State Univ., University Park
• NSA Number: NSA-29-000517
• OSTI ID: 4438106
• Journal Information: J. Mol. Biol., v. 79, no. 2, pp. 267-284, Other Information: Orig. Receipt Date: 30-JUN-74; Bib. Info. Source: UK (United Kingdom (sent to DOE from))
• Country of Publication: United Kingdom
• Language: English

Related Subjects

N48120* -Life Sciences-Radiation Effects on Biochemicals- In Microorganisms
N48310 -Life Sciences-Radiation Effects on Microorganisms-Basic Studies
*CAFFEINE- RADIOSENSITIVITY EFFECTS
*DNA- STRAND BREAKS
*MYXOMYCETES- BIOLOGICAL RADIATION EFFECTS
*STRAND BREAKS- RADIOINDUCTION
CELL NUCLEI
CESIUM CHLORIDES
COBALT 60
DILUTION
DOSE-RESPONSE RELATIONSHIPS
ESCHERICHIA COLI
EV RANGE 10-100
GAMMA RADIATION
LETHAL IRRADIATION
MITOCHONDRIA
NUCLEOSIDES
PH VALUE
PHOTON BEAMS
PYRIMIDINES
RADIOSENSITIVITY
RESPONSE MODIFYING FACTORS
SACCHAROSE
SEDIMENTATION
TRITIUM COMPOUNDS