T_4, or T4 bacteriophage, is a type of virus that specifically infects bacteria, particularly Escherichia coli. It belongs to the family of viruses known as Myoviridae and is characterized by its complex structure, which includes a head and a long tail. T_4 is well-studied in microbiology and genetics due to its role in understanding viral replication and bacterial resistance. This bacteriophage is notable for its ability to inject its genetic material into a host bacterium, leading to the production of new virus particles. T_4 has been instrumental in research related to molecular biology, including the development of techniques such as DNA sequencing and genetic engineering.