Associate Professor of Biology
Associate Professor of Biology
Theodore Gurney Jr.
Elizabeth T.G. Gurney
Department of Biology
University of Utah
Salt Lake City, Utah 84112
We are studying the ways that cells occasionally make extra copies of parts of their
DNA. Spontaneous duplication of a given gene is usually rare, less than one duplication
,rer 107 cell divisions, but duplication can have important consequences in biology and
medicine. Duplication of an essential gene gives the opportunity for mutation to an
alternate function; duplication of metabolic genes can lead to drug resistance in cancer
Integration of simian virus 40 (SV40) in mouse cells transforms the cells to a
malignant phenotype by integration of SV40 DNA in a mouse chromosome and expression of the
SV4() gene product T antigen, an important control protein involved in SV40 DNA
replication, cel1 immortalization, and malignant transformation. The integrated SV40 DNA
in SV40-transformed mouse cells undergoes spontaneous partial duplication at an
extraordinarily high rate, more than one duplication in 10^3 cell divisions. We find hih
rates of duplication near an integrated SV40 control region, a 350 nucleotide segment of
viral DNA which contains the viral origin of DNA replicatiion plus transcriptional
enhancers and promoters. L)NA that is one or tvvo genes away from the integrated control
region is duplicated much less freguently.
Our recent work provides evidence that there are two distinguishable mechanisms of
spontaneous duplication, one that is dependent on T antigen expression and another that is
independent. The evidence for duplication without T antigen is spontaneous DNA
rearrangement in mouse LMtk- cells transformedby the integrated plasmid pSV2neo. The
plasmid contains an SV40 control region but no T antigen coding sequence. No T antigen is
expressed in cells with integrated plasmid, but DNA rearrangements occur nevertheless
within integrated plasmid DNA. Spontaneous duplications are affected by sequence changes
in the SV40 control region.
The evidence for involvement of T antigen in duplication comes from comparisons between
closely related SV40-transformed cell lines. The line SVT2 has a duplication rate of about
10^-3 events/cell/division but the spontaneous SVT2 mutant X1 has a tenfold higher rate.
The differences between SVT2 and X1 include different tandem duplications of integrated
SV40 DNA, different expressed large T antigens (100 kDa vs 94 kDa), and different amounts
of 20 kDa small T antigen. X1, but not SVT2, has a tandem duplication of the SV40 control
region Using spontaneous DNA rearrangements as a mutagen, we isolated X1 mutants with
various combinations of the differences between SVT2 and X1. The property best correlated
with duplication was the kind of T antigen expressed; the 94 kDa T antigen was associated
with the higher rate and the 100 kDa T antigen was associated with the lower rate.
Gurney, T. and E.G. Gurney. 1989. Spontaneous rearrangement of integrated simian virus
40 DNA in nine transformed rodent cell lines. J. Virol. 63:165-174.
Hunter, D.J. and E.G. Gurney. 1994. The genomic instability associated with integrated
simian virus 40 DNA is dependent on the origin of replication and early control region.J.
Gurney, T. and E.G. Gurney. 1997. Spontaneous rearrangements of integrated SV40 DNA in
transformed mouse cells are more frequent in cells expressing wild-type 94 kDa large T
antigen than in mutant cells expressing 100 kDa SV40 super T antigen. Manuscript in