Ubiquitin-proteasome-dependent degradation of TBP-like protein is prevented by direct binding of TFIIA.

Although the majority of gene expression is driven by TATA-binding protein (TBP)-based transcription machinery, it has been reported that TBP-related factors (TRFs) are also involved in the regulation of gene expression. TBP-like protein (TLP), which is one of the TRFs and exhibits the highest affinity to TFIIA among known proteins, has recently been showed to have significant roles in gene regulation. However, how the level of TLP is maintained in vivo has remained unknown. In this study, we explored the mechanism by which TLP protein is turned over in vivo and the factor that maintains the amount of TLP. We showed that TLP is rapidly degraded by the ubiquitin-proteasome system and that tight interaction with TFIIA results in protection of TLP from ubiquitin-proteasome-dependent degradation. The half-life of TLP was shown to be less than a few hours, and the proteasome inhibitor MG132 specifically suppressed TLP degradation. Moreover, knockdown and over-expression experiments showed that TFIIA is engaged in stabilization of TLPin vivo. Thus, we showed a novel characteristic of TLP, that is, interaction with TFIIA is essential to suppress proteasome-dependent turnover of TLP, providing a further insight into TLP-governed gene regulation.

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