The TFIIS (TCEA1; 601425) protein is a conserved eukaryotic transcription elongation factor. Human TFIIS contains an RNA polymerase II (Pol II, see 180660)-binding domain and a zinc finger nucleic acid-binding domain. Both domains are required to stimulate transcription elongation. By screening a genomic library with oligonucleotide probes derived from conserved sequences in viral and cellular mRNA 5-prime-capping enzymes, Yeh and Shatkin (1994) identified a gene encoding p21, a protein that belongs to the SII family. The predicted 157-amino acid protein has a calculated molecular mass of 21 kD, an extremely basic pI of 11.75, and is rich in arginine, serine, and proline residues. Bipartite nuclear localization signals are located near both ends of the protein. The p21 protein is 29% identical to both human and mouse TFIIS.

Although p21 lacks the conserved zinc finger domain required in TFIIS for stimulation of transcription elongation, it does contain a zinc finger-like motif as well as a sequence related to the TFIIS Pol II-binding region. Yeh and Shatkin (1994) noted that the N-terminal region of p21 contains an arginine/serine-rich region that is closely related to the RS domain of the pre-mRNA splicing factor SC35 (600813). On Western blots of mammalian cell extracts, p21 migrated as a 27-kD protein. The authors suggested that the discrepancy between the predicted and observed molecular masses of the protein might be due to the extremely basic nature of the protein.

Using immunofluorescence, Yeh and Shatkin (1994) found that epitope-tagged p21 is predominantly located in nuclei of mammalian cells. When p21 was overexpressed in mammalian cells, it modulated transcription from various viral and cellular promoters in a promoter context-dependent fashion. For example, transcription from the c-fos (164810) promoter was increased, while Rous sarcoma virus (RSV) long terminal repeat (LTR) promoter activity was repressed by p21. Yeh and Shatkin (1994) demonstrated that both the zinc finger-like motif and the arginine/serine-rich region of p21 are essential for inhibition of RSV LTR function. The inhibition appears to occur at the RNA level and does not appear to involve direct binding of p21 to the target sequence. The authors suggested that p21 exerts its effects on the RSV LTR via protein-protein interactions with other transcriptional regulators.

Pillutla et al. (1999) reported that the p21, or TCEAL1 (TCEA-like 1), gene contains 3 exons and spans 2.1 kb. Northern blot analysis indicated that TCEAL1 was expressed as an approximately 1.2-kb mRNA in all tissues tested. An approximately 7-kb transcript was also detected in heart and skeletal muscle.

By fluorescence in situ hybridization and by inclusion in previously mapped clones, Pillutla et al. (1999) mapped the TCEAL1 gene to Xq22.1.