Bacteriophage T7

it is a model phage (phage group) that was picked out from a commercial mixture called phage therapy treatments. Though it showed promise, when antibiotics appeared, phage therapy was dropped

Complex virus  with short tail and short tail fibers; 60 nm diameter

starts off with a naked icosahedral

really ordered and intricate structures attached to the icosahedral wall; head and tail virus that physically injects contents of the virus inside its cell

• really big virus with a T=7 (7x60)
• 56 open reading frames code for 59 proteins 

has three classes of genes that are organized into blocks from left to right on the genome

linear dsDNA

they are clustered both by function and by the timing of their expression during the life cycle of the phage

Class I: needed for expression of the remainder of phage genes and to shut down host cell functions

Class II: occupy the next one-third of the genome. Most are concerned with phage DNA replication

Class III: code for phage structural proteins and proteins needed for DNA maturation and packaging

• first 6-8 minutes of infection
• control expression of phage genes and host shutoff

middle genes that control phage DNA replication

late genes

• structural proteins
• proteins for DNA maturation and packaging

Looks and behaves as a syringe

The tail fibers bind to the outer membrane of bacteria. A conformational change occurs and a core proteins form a channel through the outer membrane, wall, and cytoplasmic membrane. 850 bp of viral DNA is transported into the cell

Virus binds to lipopolysaccharide on the outer membrane

Another conformational change allows transportation of the first 850 bps of the DNA, which exposes three promoters recognized by E. coli RNA plymerase. At this point, transcription occurs, pulling the DNA into the cytoplasm. 

Therefore, RNA polymerase transfers the DNA from the capsid into the cell while making mRNA

The early genes need to be transcribed first to have a successful infection

The virus makes proteins that inhibit restriction endonucleases. 

They also make viral RN polymerase, which drives the rest of transcription of the different genes. 

Promoters recognized by the phage RNA polymerase are recognized; and, new transcripts and proteins are made

enzymes involved in T7 DNA replication, such as DNA ligase, SSBP, endonucleases, lysozyme, primase and helicases, DNA polymerase, and exonucleases (degrade host cell DNA)

• portal protein (connector for tail)
• scaffolding protein
• capsid protein
• tail protein
• core proteins

AKA: structural components

delayed entry and promoter strength

transcription-dependent DNA entry delays transcription

Class III promoters ahve a higher affinity for T7 RNA polymerase

By putting a T7 promoter in front of a gene of interest, one can make a variety of expression vectors, which allow regulated expression and high yields of genes of interest

requires a novel T7- coded RNA polymerase

• Class 1 gene 1.0 is a viral RNA polymerase that transcribes Class II and III genes
• Gene 0.3 protects viral DNA from degradation
• Gene 0.7 shuts off cellular transcription

helps to regulate gene expression