Open AccessCharacterization and Replication Control of Plasmids from Enterobacter cloacae DF 13
Author(s) -
ZANDVLIET Gerard M.,
JANSZ Hendrik S.
Publication year - 1976
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1976.tb10177.x
Subject(s) - plasmid , biology , agarose gel electrophoresis , enterobacter cloacae , escherichia coli , microbiology and biotechnology , genetics , dna , enterobacteriaceae , gene
It has been shown previously that Enterobacter cloacae DF13 harbours at least five different size classes of plasmids. A 45 × 10 6 ‐ M r self‐transmissible R factor determining resistance against tetracyclin, sulfanilamide, streptomycin and chloramphenicol, a 6.0 × 10 6 ‐ M r bacteriocinogenic factor without sex factor activity and cryptic plasmids in the size classes of M r 1.3 × 10 6 , 2.8 × 10 6 and 8.0 × 10 6 respectively. The present work deals with the determination of the homogeneity and molecular relationship of 1.3 10 6 ‐ M r (mini) and 2.8 × 10 6 ‐ M r (midi) cryptic plasmids and the 6.0 10 6 ‐ M r (maxi) bacteriocinogenic factor, their kinetics of replication and their replication control in response to inhibition of protein synthesis. It has been shown by reassociation kinetics and agarose gel electrophoresis that the maxi plasmids represent a homogeneous population of molecules without repeating sequences. Although homogeneous in size the midi plasmids show considerable heterogeneity in base sequence. The mini plasmids have been shown by agarose gel electrophoresis to consist of four subclasses with contour lengths of 0.79 μm, 0.69 μm, 0.66 μm and 0.61 μm respectively. There is less than 25 % base sequence homology between maxi, midi and mini plasmids and only partial homology within the mini size subclasses. The replication of the four mini plasmids shows absolute dependency on protein synthesis. The replication of midi and maxi plasmids proceeds in the absence of protein synthesis and is inhibited immediately after relief from arginine starvation. These results suggest that the replication of mini plasmids is under control of a positively acting protein and that of midi and maxi plasmids under control of a negatively acting protein. A common feature of these plasmids is their replication kinetics, which follow the anarchical model, i.e. to maintain a fixed number ( n ) of plasmids, n replications occur during one cell cycle the plasmids taking part at random.