TY - JOUR

T1 - Escherichia coli minichromosomes

T2 - random segregation and absence of copy number control

AU - Jensen, M R

AU - Løbner-Olesen, A

AU - Rasmussen, K V

PY - 1990/9/20

Y1 - 1990/9/20

N2 - Minichromosomes, i.e. plasmids that can replicate from an integrated oriC, have been puzzling because of their high copy numbers compared to that of the chromosomal oriC, their lack of incompatibility with the chromosome and their high loss frequencies. Using single cell resistance to tetracycline or ampicillin as an indicator of copy number we followed the development of minichromosome distributions in Escherichia coli cells transformed with minichromosomes and then allowed to grow towards the steady state. The final copy number distribution was not reached within 15 to 20 generations. If the minichromosome carried the sop (partitioning) genes from plasmid F, the development of the copy number distribution was further drastically delayed. We conclude that E. coli cells have no function that directly controls minichromosomal copy numbers, hence the absence of incompatibility in the sense of shared copy number control. We suggest that minichromosomes are subject to the same replication control as the chromosome but segregate randomly in the absence of integrated partitioning genes. This, combined with evidence that the lowest copy number classes are normally present despite high average copy numbers, can account for the high loss frequencies.

AB - Minichromosomes, i.e. plasmids that can replicate from an integrated oriC, have been puzzling because of their high copy numbers compared to that of the chromosomal oriC, their lack of incompatibility with the chromosome and their high loss frequencies. Using single cell resistance to tetracycline or ampicillin as an indicator of copy number we followed the development of minichromosome distributions in Escherichia coli cells transformed with minichromosomes and then allowed to grow towards the steady state. The final copy number distribution was not reached within 15 to 20 generations. If the minichromosome carried the sop (partitioning) genes from plasmid F, the development of the copy number distribution was further drastically delayed. We conclude that E. coli cells have no function that directly controls minichromosomal copy numbers, hence the absence of incompatibility in the sense of shared copy number control. We suggest that minichromosomes are subject to the same replication control as the chromosome but segregate randomly in the absence of integrated partitioning genes. This, combined with evidence that the lowest copy number classes are normally present despite high average copy numbers, can account for the high loss frequencies.

KW - Chromosomes, Bacterial/physiology

KW - DNA Replication

KW - Escherichia coli/genetics

KW - Plasmids

KW - Regulatory Sequences, Nucleic Acid

U2 - 10.1016/S0022-2836(05)80344-4

DO - 10.1016/S0022-2836(05)80344-4

M3 - Journal article

C2 - 2213882

VL - 215

SP - 257

EP - 265

JO - Journal of Molecular Biology

JF - Journal of Molecular Biology

SN - 0022-2836

IS - 2

ER -