page_title: Bacteriophage T12
section_title: Genome
hierarchical_section_title: Bacteriophage T12 / Genome
caption_attribution_description: English: This image shows how known genes of bacteriophage T12 are arranged once the phage chromosome has integrated into the chromosome of S. pyogenes. The green box represents the phage chromosome, while the black line represents the bacterial chromosome into which T12 integrates. The arrows in the diagram show the direction in which the genes are transcribed. The red arrows show the arrangement of the speA and int genes. The pink arrows indicate only the orientation of the serine tRNA gene into which the phage integrates. The coding region of the serine tRNA gene remains intact even after the phage integrates.
context_page_description: Bacteriophage T12 is a bacteriophage that infects the bacterial species Streptococcus pyogenes, and converts a harmless strain of bacteria into a virulent strain. It carries the speA gene which codes for erythrogenic toxin A. speA is also known as streptococcal pyogenic exotoxin A, scarlet fever toxin A, or even scarlatinal toxin. Note that the name of the gene "speA" is italicized; the name of the toxin "speA" is not italicized. Erythrogenic toxin A converts a harmless, non-virulent strain of Streptococcus pyogenes to a virulent strain through lysogeny, a life cycle which is characterized by the ability of the genome to become a part of the host cell and be stably maintained there for generations. Phages with a lysogenic life cycle are also called temperate phages. Bacteriophage T12, a member of a family of related speA-carrying bacteriophages, is also a prototypic phage for all the speA-carrying phages of Streptococcus pyogenes, meaning that its genome is the prototype for the genomes of all such phages of S. pyogenes. It is the main suspect as the cause of scarlet fever, an infectious disease that affects small children.
context_section_description: The physical map of the T12 genome was found to be circular with a total length of 36.0kb. The phage genome is reported to carry the speA gene, which is a 1.7kb segment of the phage T12 genome flanked by SalI and HindIII sites.
  The phage integrase gene (int) and the phage attachment site (attp) are located just upstream of the speA gene in the phage genome. The bacteriophage T12 integrates into S. pyogenes chromosome by site-specific recombination into the anticodon loop of a gene that codes for serine tRNA. The bacterial attachment site (attB) has a 96 base pair sequence homologous to the phage attachment site and is located at the 3’ end of the tRNA gene such that the coding sequence of the tRNA gene remains intact after integration of the prophage. Phage T12 is the first example of a phage from a gram-positive, low G-C content host that uses this kind of integration site.
caption: Arrangement of known genes of bacteriophage T12 after integration of the phage chromosome into the S. pyogenes chromosome. Green box: phage chromosome; black line: bacterial chromosome. Arrows indicate the direction of gene transcription; red arrows: arrangement of the speA and int genes; pink arrows: orientation of the serine tRNA gene into which the phage integrates. The coding region of the serine tRNA gene remains intact even after the phage integrates.
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