Recent Pulsed Field Gel Electrophoresis Data
Suggest Two Types of DSBs
Abstract
The temporal evolution of unrejoined and misrejoined DNA
double-strand breaks (DSBs) produced by high doses (80-160 Gy)
of x-rays has recently
been estimated using pulsed field gel electrophoresis (PFGE)
[Lobrich et al. Proc. Natl. Acad. Sci. 92 12050-12054 (1995)]. We compared this data to three models.
A RBM (``Revell binary misrejoining'') model, based on the usual
repair-misrepair
and lethal-potentially-lethal models, appears to be inconsistent
with the data.
The main discrepancies are the following: 1)
the RBM model predicts that 90 percent of the misrejoined DSBs form
by the time 75 percent of the DSBs have disappeared while the
data indicate that only 50 percent
are formed by this time;
and 2) the model predicts an increasing
fraction of DSBs misrejoined at 160 Gy compared to
80 Gy while the data support approximately equal fractions misrejoined.
These discrepancies are alleviated in the Sax subset (SS) and
Revell subset (RS) models. In the SS and RS models two
types (or subsets) of DSBs exist: those that are active in misrejoining
and those that are not.
In the SS model active DSBs misrejoin using
Sax's breakage-and-reunion mechanism; in
the RS model active DSBs either repair, or misrejoin according to
Revell's complete exchange misrejoining mechanism. Both models
are consistent with the data set considered.
Radiation Research 149, 52-58, 1998.
Tomas Radivoyevitch*, David G. Hoel*, Philip J. Hahnfeldt#,
Bjorn Rydberg+, and Rainer K. Sachs-.
*Department of Biometry and Epidemiology,
Medical University of South Carolina,
Charleston, SC 29425;
#Joint Center for Radiation Therapy, Harvard Medical
School, Boston, MA 02115;
+Life Sciences Division, Lawrence Berkeley National
Laboratory, University of California, Berkeley, CA 94720;
-Department of Mathematics,
University of California, Berkeley, CA 94720.
Corresponding author: Tomas Radivoyevitch, Department of Biometry and
Epidemiology,
Medical University of South Carolina,
Charleston, SC 29425 USA;
tel: 803-766-7064; fax: 803-792-0539; e-mail: radivot@musc.edu.
PFGE