title: The REC1 gene of Ustilago maydis, which encodes a 3'-->5' exonuclease, couples DNA repair and completion of DNA synthesis to a mitotic checkpoint.
abstract: Mutation in the REC1 gene of Ustilago maydis results in extreme sensitivity to killing by ultraviolet light. The lethality of the rec1-1 mutant was found to be partially suppressed if irradiated cells were held artificially in G2-phase by addition of a microtubule inhibitor. This mutant was also found to be sensitive to killing when DNA synthesis was inhibited by external means through addition of hydroxyurea or by genetic control in a temperature-sensitive mutant strain defective in DNA synthesis. Flow cytometric analysis of exponentially growing cultures indicated that wild-type cells accumulated in G2 after UV irradiation, while rec1-1 cells appeared to exit from G2 and accumulate in G1/S. Analysis of mRNA levels in synchronized cells indicated that the REC1 gene is periodically expressed with the cell cycle and reaches maximal levels at G1/S. The results are interpreted to mean that a G2-M checkpoint is disabled in the rec1-1 mutant. It is proposed that the REC1 gene product functions in a surveillance system operating during S-phase and G2 to find and repair stretches of DNA with compromised integrity and to communicate with the cell cycle apparatus.
authors.affiliation: Hearst Microbiology Research Center, Cornell University Medical College, New York, New York 10021, USA.
authors.forename: K
authors.initials: K
authors.lastname: Onel
authors.forename: A
authors.initials: A
authors.lastname: Koff
authors.forename: R L
authors.initials: RL
authors.lastname: Bennett
authors.forename: P
authors.initials: P
authors.lastname: Unrau
authors.forename: W K
authors.initials: WK
authors.lastname: Holloman
mesh_terms: D001483:Base Sequence; D002453:Cell Cycle / Q000528:radiation effects; D004249:DNA Damage; D017931:DNA Primers; D004260:DNA Repair / Q000528:radiation effects; D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000096:biosynthesis / Q000235:genetics*; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics*; D007700:Kinetics; D008938:Mitosis; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D013997:Time Factors; D014466:Ultraviolet Rays; D014588:Ustilago / Q000166:cytology / Q000235:genetics* / Q000502:physiology
chemical_list: D017931:DNA Primers; D004271:DNA, Fungal; D005656:Fungal Proteins; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V