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
SN - 0022-2836
VL - 215
SP - 257
EP - 265
JO - Journal of Molecular Biology
JF - Journal of Molecular Biology
IS - 2
ER -