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TIP120B: a novel TIP120-family protein that is expressed specifically in muscle tissues.

TATA-binding protein (TBP) forms complexes with various nuclear proteins and plays roles in all eukaryotic transcription. We previously identified TBP-interacting protein 120 (TIP120) from rat liver. TIP120 stimulates in vitro transcription generally. Homologs of TIP120 exist in various higher eukaryotes including D. melanogaster, C. elegans, and A. thaliana. Here, we isolated cDNA of a novel rat TIP120-like protein, named TIP120B. Rat TIP120B was composed of 1,235 amino acids and was 60% identical to the original TIP120 (re-named TIP120A). However, TIP120B gene was expressed specifically in the muscle tissues, which was contrary to the ubiquitous expression of TIP120A. Moreover, TIP120B protein was observed exclusively in the muscle tissues. TIP120B is therefore suggested to be a muscle-specific protein. Northern blot analysis of the mouse embryo revealed that the expression of TIP120B was temporarily increased during the embryogenesis, whereas TIP120A maintained a constant expression level. Pull-down assay using GST-fused TBP demonstrated that TBP specifically associated with TIP120B in the nuclear extract. These results indicate that TIP120B is a muscle-specific TIP120 family protein and can also interact with TBP. TIP120B is supposed to have a specific role in muscle tissues, which may be diffrerent from that of TIP120A.