M.Sc Thesis

M.Sc StudentMarom Inbal
SubjectBlue Light Regulation of DNA Photolyase Gene Expression
in Filamentous Fungi
DepartmentDepartment of Biology
Supervisor PROF. Benjamin Horwitz


Photolyase is a DNA repair enzyme that utilizes blue light for repairing UV-induced damage. In this study, two fungal DNA photolyase homologs were cloned and sequenced. Light treatments were tested for their effect on fungal photolyases: continuous white light, a rapid blue light pulse, and continuous dark. Blue light is thought to serve as a warning signal: exposure to blue light might indicate an exposure to shorter and more damaging wavelengths. Photolyase, which repairs UV photoproducts, is thus rapidly induced. Photolyase was rapidly induced after a blue pulse in Aspergillus nidulans but not in Cochliobolus heterostrophus, in which its transcript level was similar in all treatments. The transformation of Trichoderma harzianum (in which photolyase is light regulated) photolyase promoter fused to a reporter gene into Cochliobolus heterostrophus resulted in blue light induction of the reporter gene. This indicates that the promoter region is involved and that the mechanism which is needed for blue light reception and photolyase induction still exists in Cochliobolus heterostrophus. The specific mechanism of photolyase induction by blue light is not known yet. Aspergillus nidulans mutants were examined for their photolyase induction. Velvet A (veA) and fluG genes were not found to be involved in photolyase induction. The lack of any of three genes that participate in the first step of molybdenum cofactor biosynthesis resulted in lack of blue light regulation of photolyase. StuAp (a repressor in Aspergillus nidulans) mutant had no blue light regulation of photolyase. StuAp could be an activator for blue light induction of photolyase.