Escherichia coli K-12 F-prime factors, old and new.

A series of mutants of E coli temperature-sensitive for DNA synthesis has been studied The temperature-sensitive DNA mutations map in seven distinct genetic loci most of which have not been previously reported Mutations in dnaA and in dnaC affect the initiation of DNA replication; those at the remaining loci affect chain elongation A temperature-sensitive F′lac is shown to suppress a group A mutant with somewhat less efficiency than other F′ factors previously reported by others The gene products rendered temperaturesensitive by the mutations have not been identified for any of the loci

Escherichia coli mutants temperature-sensitive for DNA synthesis.

The ampicillin resistance (β-lactamase) determinant of RP4 can be transposed onto various other replicons genetically unrelated to RP4 including several but not all R factors.

Transposition of ampicillin resistance from RP4 to other replicons.

INTRODUCTION AND DEFINITIONS ...................................... 361 SOME PROPERTIES OF BACTERIAL PLASMIDS .......................... 362 Chromosomal Integration ............... .................................... 363 Fertility Repression........................................................ 363 Incompatibility ............................................................. 364 Elimination ................................................................ 364 Replication and Segregation (Membrane Site Model) ...... ................... 365 GENETICS AND LINKAGE OF PLASMID-BORNE GENES ................. 366 MOLECULAR MODELS FOR PLASMIDS AND THEIR IMPLICATIONS FOR THE EVOLUTION OF R FACTORS.367 PHYSICAL COMPOSITION AND FORM .................................... 369 METHODS OF ISOLATION ................................................. 371 Differences from Host DNA Base Ratio ................................... 371 From Minicells ............................................................. 372 Lysis with Nonionic Detergent (Brij 58) ......... ............................ 373 Conjugal Transfer.......................................................... 373 Isolation of CCC Plasmid Molecules 374 Cellulose nitrate adsorption ............ ................................... 374 Alkaline sucrose sedimentation ........................................... 374 Ethidium bromide-cesium chloride centrifugation ...... .................... 374 METHODS OF MOLECULAR WEIGHT DETERMINATION ................. 374 Sedimentation Analysis ................. .................................... 374 Loss of Supercoil Structure by Irradiation ........ ........................... 375 Reassociation Kinetics...................................................... 376 Electron Microscopy ....................................................... 376 SIZE AND CONFIGURATION ............ .................................. 376 F and F' Sex Factors.376 Colicinogenic Factors ....................................................... 379 Drug-Resistance Factors ............... ................................... 380 Monomolecular factors ............... .................................... 380 Unstable R factors ....................................................... 381 Multimolecular R factors .............. ................................... 382 PHYSICAL INTERRELATIONSHIPS ........................................ 384 MOLECULAR STRUCTURE ..... ............................................ 385 Monomolecular Plasmids .......................... 385 A Revised Map for R222 .................... 387 Alternative Molecular Structures ofR Factors 387 Speculations on R-Factor Evolution ....... ................ 389 ASPECTS OF PLASMID REPLICATION ............ ........................ 390 Plasmid Copy Number-Relaxed and Stringent Regulation.390 Mechanism of Relaxed Replication.391 "Transition" in Drug Resistance ................ ............. 392 DNA-Protein "Relaxation Complexes"......................................... 393 Replication in Minicells ........... ............................ 394 Transfer Replication .......... ............................. 394 CONCLUSIONS ........................................... 395 LITERATURE CITED .......... ............................. 397

Molecular structure of bacterial plasmids.

Members of the five classes of temperature-sensitive simian virus 40 mutants were tested for their ability to transform Chinese hamster lung cells. Two criteria for transformation were used: the ability to form clones in medium with low serum concentrations and the ability to overgrow a monolayer. Only A mutants failed to transform at the restrictive temperature when subconfluent Chinese hamster lung monolayers were used. However, both A and D mutants failed to transform at the restrictive temperature when confluent monolayers and depleted medium were used. When transformed clones were selected, purified by recloning, and examined at both temperatures, only cell lines induced by A mutants lost the transformed phenotype at the higher temperature. Thus, A function is required for maintenance of the transformed phenotype in Chinese hamster lung cells. A function is known to be required for the initiation of viral DNA synthesis in permissive cells. Therefore, transformation may be a consequence of the introduction into a cell of the capacity for aberrant initiation of DNA replication.

Yukinobu Nishimura

Papers

Chromosome replication in Escherichia coli. IV. Control of chromosome replication and cell division by an integrated episome.