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Updated: Aug 15, 2026
Electrophoretic Analysis of Replication Through Structure-Prone DNA Repeats Within the SV40-Based Human Episome
Published on: September 13, 2024
Distinct patterns of MCM protein binding in nuclei of S phase and rereplicating SV40-infected monkey kidney cells
Thomas D Friedrich1, Elzbieta Bedner, Zbigniew Darzynkiewicz
1Albany Medical College, Center for Immunology and Microbial Diseases, Albany, New York 12208, USA. friedrt@mail.amc.edu
Background:
Simian Virus 40 (SV40) infection of growth-arrested monkey kidney cells stimulates S phase entry and the continued synthesis of both viral and cellular DNA. Infected cells can attain total DNA contents as high as DNA Index, DI = 5.0-6.0 (10-12C), with host cell DNA representing 70-80% of the total. In this study, SV40-infected and uninfected control cells were compared to determine whether continued DNA replication beyond DI = 2.0 was associated with rebinding of the minichromosome maintenance (MCM) hexamer, the putative replicative helicase, to chromatin.
Method:
Laser scanning cytometry was used to measure the total expression per cell and the chromatin/matrix-association of two MCM subunits in relation to DNA content.
Results:
MCM2 and MCM3 proteins that were associated with the chromatin/matrix fraction in G1 phase of both uninfected and SV40-infected cells were gradually released during progression through S phase. However, in SV40-infected cells that progressed beyond DI = 2.0, chromatin/matrix-associated MCM2 and MCM3 remained at the low levels observed at the end of S phase. Rereplication was not preceded by an obvious rebinding of MCM proteins to chromatin, as was observed in G1 phase.
Conclusions:
The rereplication of host cell DNA in the absence of the reassociation of MCM proteins with chromatin indicates that SV40 infection induces a novel mechanism of licensing cellular DNA replication.
