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Amazing genome structure: Why does T4 bacteriophage have 289 proteins? What does it mean?
Escherichia virus T4 is a bacteriophage that infects Escherichia coli. The complexity of its genome structure has attracted widespread attention from scientists. This double-stranded DNA virus is part of the subfamily Tevenvirinae and belongs to the family Straboviridae. Unlike some bacteriophages, T4 virus can only undergo a lytic life cycle and is incapable of a lysogenic life cycle.
The predecessor of T4 phage was once called T-even phage, which includes several other strains such as T2 and T6. Since the 1940s, T-even phage has been regarded as one of the best model organisms. Why has a highly complex virus with nearly 300 genes become the center of research? This reflects significant advances in biological research in understanding the genetics and biology of viruses.
"The genome of bacteriophage T4 is approximately 169 kbp long and encodes 289 proteins, showing its high genomic complexity."
The genome of T4 has end redundancy, which means that the long multi-genome chain formed during DNA replication can be cut into several genomes at unspecified positions, and these genomes are circularly arranged. . The latest research has found that the T4 genome contains intron sequences similar to those of eukaryotes. How does this genome structure affect the function of T4 and what is its significance in the evolution of the virus?
The protein composition of the T4 virus is key to its ability to successfully attack and infect bacteria. Its structure consists of an icosahedral head (i.e., capsule) about 90nm wide and 200nm long and a complex tail. The tail's special structure enables T4 to effectively recognize the surface receptors of E. coli and inject its own DNA into the cell.
"The tail structure of the T4 virus is more complex than that of most known bacteriophages, which makes it more adaptable during infection."
During the infection process, the T4 virus first binds to the surface receptors of the E. coli cell (such as OmpC porin and lipopolysaccharide) through the long tail fiber (LTF) heel. When binding occurs, a recognition signal is emitted, causing the short tail fiber (STF) to irreversibly attach to the cell surface. Subsequently, the pressure caused by the contraction of the tail sleeve causes the tail of the virus to pierce the bacterial outer membrane, completing the injection of the genome.
During this infection process, T4 attempts to acquire the host cell's resources for its own reproduction. The lytic cycle of T4 takes about 30 minutes at 37°C, which means that once infection occurs, a large number of progeny phages are produced rapidly, with up to 100 to 150 new virus particles released per infected host cell.
"The lytic cycle proceeds with high efficiency, allowing T4 to rapidly multiply and spread within its host."
As the research deepened, scientists discovered that T4 phage not only has the ability to effectively reproduce viruses, but also has a very unique gene repair mechanism. In 1946, Salvador Luria proposed the multiplicity reactivation (MR) process, in which two or more viral genomes interact to form a complete viral genome, a phenomenon that hinted at the universality of DNA repair.
Looking back at the history of T4 phage, since Fredrick Twort and Félix d'Hérelle discovered bacteriophage in the early 20th century, this field has made remarkable progress. As research progressed after World War II, T4 became central to numerous breakthroughs in biology and genetics, laying the foundation for the research of several Nobel Prize winners.
In summary, the complex structure of more than 289 proteins of T4 phage is not only the key to its successful infection, but also has far-reaching significance in decoding biological genetics and developmental virology. This got us thinking, how might such genetic complexity affect the evolution and survival of other life forms?
