Genomics, evolution, and expression of TBPL2, a member of the TBP family

TBPL2 is the most recently discovered and less characterized member of the TATA box binding protein (TBP) family that also comprises TBP, TATA box binding protein-like 1 (TBPL1), and Drosophila melanogaster TBP related factor (TRF). In this paper we report our in silico and in vitro data on (i) the genomics of the TBPL2 gene in Homo sapiens, Pan troglodytes, Mus musculus, Rattus norvegicus, Gallus gallus, Xenopus tropicalis, and Takifugu rubripes; (ii) its evolution and phylogenetic relationship with TBP, TBPL1, and TRF; (iii) the structure of the TBPL2 proteins that belong to the recently identified group of the intrinsically unstructured proteins (IUPs); and (iv) TBPL2 expression in different organs and cell types of Homo sapiens and Rattus norvegicus. Similar to TBP, both the TBPL2 gene and protein are bimodular. The 3' region of the gene encoding the DNA binding domain (DBD) was well conserved during evolution. Its high homology to vertebrate TBP suggests that TBPL2 also should bind to the TATA box and interact with the proteins binding to TBP carboxy-terminal domain, such as the TBP associated factors (TAFs). As already demonstrated for TBP, TBPL2 amino-terminal segment is intrinsically unstructured and, even though variable among vertebrates, comprises a highly conserved motif not found in any other known protein. Absence of TBPL2 from the genome of invertebrates and plants demonstrates its specific origin within the subphylum of vertebrates. Our RT-PCR analysis of human and rat RNA shows that, similar to TBP, TBPL2 is ubiquitously synthesized even though at variable levels that are at least two orders of magnitude lower. Higher expression of TBPL2 in the gonads than in other organs suggests that it could perform important functions in gametogenesis. Our genomic and expression data should contribute to clarify why TBP has a general master role within the transcription apparatus (TA), whereas both TBPL1 and TBPL2 perform tissue-specific functions.