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TBX2 is a T-box transcription factor involved in developmental control of cellular identity and proliferation. In the developing heart, it contributes to regional gene programmes that distinguish specialized territories from chamber myocardium. It is related to TBX3 but the two factors are not interchangeable in every context. Shared DNA-binding-family membership therefore does not establish identical expression or developmental function. ^[ref]

TBX3 is a T-box transcription factor with developmental roles including limb, gland and cardiac patterning. It can repress or activate gene programmes depending on its molecular partners and regulatory context. Its developmental importance illustrates how one DNA-binding regulator can act in several organs at different times. A phenotype following altered expression therefore needs a specified tissue and stage before it can be assigned to one direct target. ^[ref]

Transthyretin is a secreted transport protein that forms a tetramer and carries thyroid hormones in blood plasma and cerebrospinal fluid. It also associates with retinol-binding protein, contributing to transport of vitamin A. The transported small molecule and the carrier have different roles: binding changes distribution and availability rather than turning the carrier into a thyroid hormone. ^[ref]

Transthyretin also illustrates the link between assembly and disease. Destabilization and misassembly can produce amyloid deposits. Functional transport by a soluble tetramer and accumulation of aggregated material are different molecular states, so detecting the same protein sequence does not establish that it remains in its normal assembly.