The REC1 gene of Ustilago maydis, which encodes a 3'-->5' exonuclease, couples DNA repair and completion of DNA synthesis to a mitotic checkpoint.
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.
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Hearst Microbiology Research Center, Cornell University Medical College, New York, New York 10021, USA.
Koff
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Bennett
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Unrau
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Holloman
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WK
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
D017931:DNA Primers; D004271:DNA, Fungal; D005656:Fungal Proteins; D005090:Exodeoxyribonucleases; D043211:Exodeoxyribonuclease V