Transcription factor IIIB: An important determinant of biosynthetic capacity that is targeted by tumour suppressors and transforming proteins.

Transcription factor IIIB (TFIIIB) is an important determinant of the biosynthetic capacity of cells, controlling the production of essential products such as tRNA and 5S rRNA. It is therefore not surprising that this factor is subject to tight regulation, in order to tailor its activity to metabolic demands. For example, TFIIIB can be strongly regulated during differentiation and is also subject to cell cycle control. The unrelated tumour suppressors RB and p53 both exert inhibitory influences upon TFIIIB. In contrast, several viruses have been shown to activate TFIIIB, including HBV and HTLV-1. The fact that cells possess multiple mechanisms for restraining the activity of TFIIIB, whereas oncogenic viruses act to subvert these controls, provides a clear indication of the significance of this factor. Deregulation of TFIIIB may be a significant step towards tumour development.