Molecular structure of bacterial plasmids.

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