Bacterial viruses

• Very complex shape, requiring 20 gene products for assembly

• - Capsid (head), contains linear dsDNA genome

• - Tail, consists of sheath plus internal tube

Bacteriophage T4

Figure 11.2

• Phage T4 binds to E. coli by contact between its tail fibers and the outer membrane.

• - A conformational change causes sheath to contract and inject the genome into the cell.

Bacteriophage T4

Figure 11.4

Fig. 10-15

NucleasesDNA polymeraseNew sigma factors

Phage DNA

Infection

Early mRNA

Early proteins

Phage DNA replication

Middle mRNA Late mRNA

Late proteinsMiddle proteins

Self assembly

Phageheadproteins

Tail, collar, baseplate, and tailfiber proteins

Mature phage particleT4 lysozymeproduction

Lysis

252015Minutes

1050

• Progeny genomes are linked in a concatemer.

• - Cut with an offset, so that individual linear genomes have slight overlaps

Figure 11.7

Figure 11.6

Replicative Cycle of Bacteriophage T4

• Progeny genomes are linked in a concatemer.

• - Cut with an offset, so that individual linear genomes have slight overlaps

Figure 11.7

• Each phage particle is assembled by convergence of three pathways involving head, tail, and tail fibers.

Figure 11.8

Figure 11.6

Replicative Cycle of Bacteriophage T4