Medical Microbiology

Bacteriophages 183

Composition...............................................

Phagesaremadeupofproteinandnucleicacid.Theproteinsformthehead,

tail,andothermorphologicalelements,thefunctionofwhichistoprotectthe

phagegenome.Thiselementbearsthegeneticinformation,thestructural

genesforthestructuralproteinsaswellasforotherproteins(enzymes)re-

quiredtoproducenewphageparticles.Thenucleicacidinmostphagesis

DNA,whichoccursasasingleDNAdoublestrandin,forexample,Tseries

phages.Thesephagesarequitecomplexandhaveupto 100 differentgenes.

Insphericalandfilamentousphages,thegenomeconsistsofsingle-stranded

DNA(example:UX1 7 4).RNAphagesarelesscommon.

TPhages

Head

Tail

DNA

Collar

Tail tube

Tail sheath

(contractile)

Tail fibers

a Base plate with tail pins

Fig.3. 25 aMorphologyof

aTseriesphage(complex

structure).

b Electron microscopic

imageofTbacteriophages.

Left: intact, infectious

phage.Right:phageshell

after injection of the

genomewithphagehead

emptyandtailsheathcon-

tracted.

3

Kayser, Medical Microbiology © 2005 Thieme