E.coli Lecture 3 Flashcards
What does the efficency of a phage infection in E.coli depend on?
If lamba lysate was grown on same media as E.coli
Why does phage need to grow on same media as E.coli?
Phage DNA is specifically modified by the host.
If DNA is not modified it is restricted
What types of Restriction Modification Systems Exist?
Type 1
Type 2
Type 3
Type 4
What is Type 2 Restriction Modification?
cleavage of DNA at the specific DNA-binding site
-> restriction enzymes used for DNA cloning
What is Type 1 Restriction Modification?
cleavage of DNA at unspecific sequences, far away from the specific DNA-binding site
What is Type 3 Restriction Modification?
cleavage of DNA at unspecific sequences close to the specific DNA-binding site
What is Type 4 Restriction Modification?
cleavage of DNA after binding to a methylated specific DNA-binding site
(MDRS modification-dependent restriction enzymes)
What are some characteristics of Restriction Modification Systems?
Strain specific:
Belong to the variable gene pool
Can be encoded on phages and mobilizable plasmids
What do RMS (restriction modification systems) do?
prevent incorporation of foreign DNA
Limit HGT
Have implications in DNA cloning
CRIPSER Cas is part of which genome?
The core genome
but can be mobilized
How do the restriction modification systems cut?
Bind to specific DNA sequence and pull DNA through and then cut based on type.
Where are MGE inserted?
At hotspots
Where are defense systems normally found
at hotspots (hence they are clustered)
How does CRISPER Cas work
CRISPER Cas genes have the Cas genes and spacer with repeats. Now phage infects the cells and almost all bacteria die but some bacteria manage to cut the phage DNA and insert this DNA into their spacer region. This spacer region can then be processed by Cas to upon reinfection cut the phage DNA quickly
How does spacer aquisition work?
- New spacer from phage
- repeats are cut via Cas
- crRNA processing
- crRNA assembly and surveillance
- Target degradation
