Replication of the R Factor R ts 1 in Proteus mirabilis

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Abstract
The replication of the R factor R ts 1 in Proteus mirabilis was examined by using the technique of CsCl density-gradient centrifugation. The proportion of R ts 1 deoxyribonucleic acid (DNA) relative to the host chromosomal DNA (% R-DNA) was 7% in both exponential and stationary growth phases in Penassay Broth and supplemented M9 minimal medium at 30 C. The chromosomal DNA content per cell varied over a threefold range in the different growth media. In agreement with previous genetic observations, the replication of R ts 1 was found to be temperature-sensitive and R ts 1 DNA was diluted from the cells during exponential growth at 42 C. 14 N- 15 N medium transfer experiments have shown that individual copies of R ts 1 are selected at random for replication during the duplication of the multicopy episome pool.