GRIP1tau, a novel PDZ domain-containing transcriptional activator, cooperates with the testis-specific transcription elongation factor SII-T1.

SII-T1 is a tissue-specific member of the transcription elongation factor S-II that is expressed specifically in male germ cells. In the present study, we have identified a protein named GRIP1tau interacting with SII-T1 by yeast two-hybrid screening. GRIP1tau is a novel isoform of glutamate receptor-interacting protein 1 (GRIP1) that associates with the cytoplasmic domain of the alpha-amino-3-hydroxy-5-methyl-4-isoaxazolepropionate (AMPA)-type glutamate receptor. GRIP1tau is a testis-specific nuclear protein that activates transcription when fused with a GAL4 DNA binding domain in GAL4-responsive reporter gene assays. The transactivation domain of GRIP1tau overlapped with the region essential for interaction with SII-T1, as revealed by co-immunoprecipitation assays. Also, transactivation by GRIP1tau was stimulated by SII-T1 in a dose-dependent manner. Therefore, we propose that GRIP1tau is a novel testis-specific transcriptional activator regulated by interaction with the testis-specific transcription elongation factor SII-T1.

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