Post-segregational killing by restriction modification gene complexes: observations of individual cell deaths.
Through a mechanism known as post-segregational killing, several plasmids mediate their stable maintenance by carrying genes that kill plasmid-free segregant cells. We demonstrated earlier that loss of plasmids carrying type II restriction modification (RM) gene complexes inhibits the propagation of a cell population and causes chromosome breakage. We now show the morphology of individual cells changes following loss of thermosensitive plasmids carrying EcoRI RM or PaeR7I RM after a shift to a non-permissive temperature. After a lag, many cells formed long filaments containing multiple nuclei as detected by DAPI staining. Several hours after the shift, many of these long filaments lacked nuclei. Fragmentation of chromosomal DNA down to 5 kb was detected by electrophoresis. These observations lend strong support to the concept of post-segregational cell killing by type II restriction modification gene complexes.
Handa
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N
Department of Molecular Biology, Institute of Medical Science, University of Tokyo, Shiroganedai, Tokyo 108-8639, Japan.
Kobayashi
I
I
D053938:DNA Fragmentation; D019175:DNA Methylation; D004261:DNA Replication; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific / Q000235:genetics*; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics* / Q000378:metabolism; D005798:Genes, Bacterial; D010957:Plasmids / Q000235:genetics*; D013696:Temperature
D004269:DNA, Bacterial; D015252:Deoxyribonucleases, Type II Site-Specific