Functional substitution for TAFII250 by a retroposed homolog that is expressed in human spermatogenesis

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Abstract
TAF II 250, the largest subunit of the general transcription factor TFIID, is expressed from the human X chromosome, at least in somatic cells. In male meiosis, however, the sex chromosomes are transcriptionally silenced, while the autosomes remain active. How then are protein-encoding genes transcribed during human male meiosis? Here we present a novel autosomal human gene, TAF1L , which is homologous to TAFII250 and is expressed specifically in the testis, apparently in germ cells. We hypothesize that during male meiosis, transcription of protein-encoding genes relies upon TAF1L as a functional substitute for TAF II 250. Like TAF II 250, the human TAF1L protein can bind directly to TATA-binding protein, an essential component of TFIID. Most importantly, transfection with human TAF1L rescued the temperature-sensitive lethality of a hamster cell line mutant in TAFII250 . TAF1L lacks introns and evidently arose by retroposition of a processed TAFII250 mRNA during primate evolution. The observation that TAF1L can functionally replace TAF II 250 provides experimental support for the hypothesis that during male meiosis, autosomes provide cellular functions usually supplied by the X chromosome in somatic cells.

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