GENETIC AND MOLECULAR ANALYSIS OF DNA DAMAGE REPAIR AND TOLERANCE PATHWAYS - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 108

human cells for repair of abasic sites in human cells is Apel, a 5' endonuclease that
specifically cleaves DNA (which is then repaired by nucleotide excision repair).
Figure 5. Repair of an oxidized base by base excision repair.
6. Principles of Molecular Dissection of DNA Repair Deficiencies
The molecular origin and the biological importance of different DNA repair paths can
be explored by a variety of approaches. We consider here two approaches, in quite
different systems. First, determining the molecular origin of a UV sensitive rice strain,
the UV radiation sensitivity was known, but the origin of this sensitivity was not
understood. There were many possible origins of the UV sensitivity, including several
that were unrelated to DNA damage or repair, and the candidate genes were neither
identified, cloned or sequenced [2, 3]. Second, the sequence of a cloned DNA repair
gene was examined in DNA samples from 124 normal humans. Since the biochemistry
of the resulting protein was well understood, the portions of the gene whose alteration
was expected to alter the function of the enzyme was known, and the potential impact of
any polymorphisms could be anticipated and compared with actual activity of the
altered gene product when expressed in Escherichia coli cells [4]. We will examine the
approaches used in both these cases.
7. UV Sensititive Rice: Norin 1
Rice cultivar Norin 1 is an ancestor of many Japanese commercially-important rice
strains.
Figure 6. UV sensitive Norin 1 grown in the absence (1) and presence (2) of supplemental UVB radiation, and
UV resistant Sasaniskiki grown in the absence (3) and presence (4) of UVB.