T4

T4 is an abbreviation used for several distinct concepts across biology and computing. The term can refer to the thyroid hormone thyroxine, the bacteriophage known as T4 that infects Escherichia coli, and the Text Template Transformation Toolkit used in Microsoft development tools. Each usage belongs to a different field and has its own defining features.

Thyroxine, or tetraiodothyronine, is the primary hormone produced by the vertebrate thyroid gland. It is formed by attaching four iodine atoms to the amino acid tyrosine within thyroglobulin and is released into the bloodstream in a relatively stable form before being converted to the more active hormone triiodothyronine (T3) in tissues. T4 circulates largely bound to transport proteins and plays a key role in regulating metabolism, growth, and development. Abnormal T4 levels can indicate thyroid disorders such as hypothyroidism or hyperthyroidism.

The T4 bacteriophage is a well-studied virus that infects Escherichia coli. It belongs to the tailed double-stranded DNA phages and is characterized by an icosahedral head and a contractile tail. The phage has a lytic life cycle and a relatively large genome that encodes hundreds of proteins involved in DNA replication, transcription, and virion assembly. T4 has been used extensively as a model system in molecular biology and genetics.

T4 templates refer to the Text Template Transformation Toolkit, a code and text generation feature found in some Microsoft development environments. Developers author T4 templates that mix fixed text with control blocks and expressions to produce output such as source code or configuration files. Templates can be processed to generate repetitive or boilerplate content automatically, improving consistency and productivity.