N

Trimethoprim °h is an analog of. I CH2OH

dIHYDROPTERIDINE (part of folic acid)

Many bacteria make toxic proteins—bacteriocins—to kill closely related bacteria that compete for the same resources.

Bacteriocins are usually encoded on plasmids. These provided the starting point for many genetic engineering vectors.

FIGURE 16.17 ColE1 is an Example of a Colicin Plasmid

The ColE1 plasmid of E. coli carries genes for colicin E1 (cea), immunity to colicin E1 (/mm) and the kil gene, required for liberation of colicin from the producer cell. The Rom gene is involved in copy number control as discussed above. ColE1 is the basis for many plasmids used in genetic engineering. The mobilization genes allow ColE1 to be transferred from cell to cell during conjugation mediated by the F plasmid.

cOLICIN El GENE - cea i kil - required for cell lysis and colicin

^ release cOLICIN El GENE - cea i

Origin region

Mobilization genes

- required for mobilization by F- plasmid

Origin region

Mobilization genes

- required for mobilization by F- plasmid

Gene for

Rom protein

Gene for

Rom protein

The ability to make bacteriocins is usually due to the presence of a plasmid in the producer cell. The best known examples are the three related ColE plasmids of E. coli, ColEl (Fig. 16.17), ColE2 and ColE3. These are small plasmids that exist in 50 or more copies per cell and have been used to derive many of the cloning vectors used in genetic engineering (see Ch. 22). These cloning vectors have the actual colicin genes removed. A variety of other colicin plasmids also occur, including the ColI and ColV plasmids. These are large single-copy plasmids and are usually transferable from one strain of E. coli to another. Many ColI and ColV plasmids also carry genes for antibiotic resistance.

The two most popular modes of action for bacteriocins are:

a) damaging the cell membrane or b) destroying nucleic acids.

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