DNA-binding protein that regulates the transcription of several genes and is involved in heart development and limb pattern formation. May bind to the core DNA motif of promoters. Monomer. Homodimer (via the T-box); binds DNA as homodimer. Shuttles between the cytoplasm and the nucleus. In late neurulae (stage 19), expression seen within the eye anlagen, with higher levels dorsally. At early tail bud stage (stage 25), expressed in each developing eye and in the heart primordia, located ventrally. In stage 26 embryos, the Tbx5-expressing cells of the heart primordia are seen to converge at the ventral midline, while expression also seen in two bilateral groups of cells continuous with and extending dorsally from the heart primordia. Expression in the dorsal region of the eye found to be maintained until early tadpole stages (stage 40), although expression becomes greatly restricted between stages 33 and 40. At stage 31/32, strong expression detected in the posterior region of the heart tube. After looping of the heart, a higher level of expression detected in the ventricle than in the atrium. The T-Box domain binds to double-stranded DNA.