MBE Advance Access published online on February 25, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msp030
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Research Article |
Molecular evolution of the testis TAFs of Drosophila
1 Harvard Medical School, Biological and Biomedical Sciences Program, Boston, MA 02115, USA
2 Department of Biology, Stanford University, Stanford, CA 94305, USA
3 Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
* Corresponding author Victor Li (victorli{at}fas.harvard.edu), Address: 107 Avenue Louis Pasteur Box 182, Boston MA 02115, Telephone: 650-224-9431, Fax: 617-432-5012
Received for publication November 28, 2008. Revision received January 25, 2009. Accepted for publication February 3, 2009.
The basal transcription machinery is responsible for initiating transcription at core promoters. During metazoan evolution, its components have expanded in number and diversified to increase the complexity of transcriptional regulation in tissues and developmental stages. To explore the evolutionary events and forces underlying this diversification, we analyzed the evolution of the Drosophila testis TAFs, paralogs of TBP-associated factors (TAFs) from the basal transcription factor TFIID that are essential for normal transcription during spermatogenesis of a large set of specific genes involved in terminal differentiation of male gametes. There are five testis specific TAFs in Drosophila, each expressed only in primary spermatocytes and each a paralog of a different generally expressed TFIID subunit. An examination of the presence of paralogs across taxa as well as molecular clock dating indicate that all five testis TAFs likely arose within a span of 
38 million years 63-250 million years ago by independent duplication events from their generally expressed paralogs. Furthermore, the evolution of the testis TAFs has been rapid, with apparent further accelerations in multiple Drosophila lineages. Analysis of between-species divergence and intra-species polymorphism indicate that the major forces of evolution on these genes have been reduced purifying selection, pervasive positive selection and coevolution. Other genes that exhibit similar patterns of evolution in the Drosophila lineages are also characterized by enriched expression in the testis, suggesting that the pervasive positive selection acting on the tTAFs is likely to be related to their expression in the testis.
Key Words: general transcription machinery • evolutionary diversification • gene duplication • testis TAF • transcription complex origin