文档介绍：Chapter 8 Bacterial ics
Plasmids
Transposons and Insertion Sequences
Bacterial Genome
Plasmids
1-1000 KB in size
Typical plasmid 1/20 of chromosome
Most are circular double-stranded DNA, some linear ds DNA
Transmitted from cell to cell via conjugation process
Some can integrated into chromosome
Can carry a variety of genes for production of toxin, resistance to antibiotics and heavy metals et al.
Circular ic elements that reproduce autonomously and have an extra-chromosomal existence:
Plasmid
Conjugative: plasmids which govern their own transfer by cell-to-cell contact are called conjugative
Tra region: a set of genes within the plasmid that control the transmissability by conjugation
Hfr (high frequency of bination): strains of bacteria that transfer large amounts of chromosomal DNA during conjugation
Supercoil: plasmids isolated from the cells are in supercoiled configuration
Plasmid separation: by ultracentrifugation or electrophoresis
Curing of plasmids: elimination of plasmids from host cells by various treatments.
Plasmids
Replication: Most plasmids of gram-positive bacteria replicate by a rolling circle mechanism.
Copy number: The number of plasmids in a cell, can range from only 1-3 copies to 100 copies.
patibility: Two different types of plasmids can not coexist in a cell.
Episomes: Plasmids having the ability to integrate into host chromosome
F-Plasmid-Fertility Plasmids
100 KB
Can be cured with acridine orange
patibility (inc)
Origin of replication (oriS)
Transposable elements (Tn)
tra region
phi: phage inhibition
IS (insertion sequence)
rep: replication functions
Cell to Cell Transfer of Plasmids
Conjugative: Plasmids that govern their own transfer by cell-to-cell contact are called conjugative (not all plasmids are conjugative)
Some conjugative plasmids can transfer ic information between distintly anisms (between gram-positive and gram-negative bacteria, between bacteria and plant cells, and between bacteria and fungi), it i