Lecture 12 Flashcards
What does control of plasmid replication determine and how does it typically occur?
Control of plasmid replication primarily involves oriV (replication origin) and rom(encodes regulatory protein) will determine the plasmid copy number and incompatibility, this generally works through plasmid DNA replication controlled by a plasmid encoded inhibitor that acts at oriV, as the cell size increases this inhibitor concentration decreases and plasmid replication will initiate. This replication results in further copies of inhibitor gene and more inhibitor, wihich limits plasmid replication further.
How do incompatible plasmids occur?
Incompatible plasmids share the same regulatory mechanism and are therefore subject to each other’s inhibitor, one will eventually gain the upper hand and eliminate the other.
What are RNA II and I in relation to plasmid replication control?
RNA II binds to oriV to initiate replication, in presence of Rom(Rop) protein RNA I binds to RNA II, preventing it from binding to oriV. Hence concentration of RNA I and Rom protein is critical. A persistent RNA II/DNA hyrid is required in order to initiate replication, in order to do this RNA II has a secondary structure which allows it to fold in a way which allows it to attach to the DNA. RNA I will destroy this loop when able to bind with the help of a Rom dimer (RNA kissing).
How does control of F plasmid replication occur?
Control of F plasmid replication is mediated by RepA proteins binding to oriV to initiate replication, at high concentrations RepA also binds to iteron sequences and “hand-cuffs” plasmids together, preventing replication until plasmids are separated at cell division.
How does oligomerisation occur and how is this problem solved?
Multimeric plasmids (oligomerisation) are formed by homologous monomeric plasmids undergoing recombination, this means they are bigger and have a higher chance of losing the plasmd during cell division, this is solved by plasmid-encoded site-specific recombination systems.
How does control of plasmid-free cells occur?
Control of plasmid-free cells: metabolic stress imposed by plasmid may slow growth of host so that plasmid free segregants out grow plasmid-bearing cells, hence the plasmid-free segregants must be killed through toxin-antitoxin systems (genetic addiction systems/post-segregational killing systems, the plasmid produces both a toxin and a less stable antitoxin, meaning when gone the toxin is able to win and kill the cell).
What is the hok/sok system?
The hok/sok system involves Hok(host killing), encodes killer peptide of 52 amino acids, it is translated from stable messenger RNA (20 minute half-life), Sok is an unstable antisense RNA (5 minute half life), it binds to gok mRNA and prevents its translation.
