IDENTIFICATION OF NOVEL GENES ENCODING TRANSCRIPTION ELONGATION-FACTOR TFIIS (TCEA) IN VERTEBRATES - CONSERVATION OF 3 DISTINCT TFIIS ISOFORMS IN FROG, MOUSE, AND HUMAN

We report the characterization of cDNA clones that define a new, third isoform of the transcription elongation factor TFIIS in Xenopus, mous e, and human. In Xenopus the mRNA of this isoform, termed TFIIS.h, sho ws tissue-restricted expression, frequently contains unspliced introns , and is characterized by three near-perfect 150-bp repeats at the 5'- terminus. Although we were unable to isolate full-length cDNAs, it is clear that these repeats contain an open reading frame encoding a regi on of TFIIS.h that is much more complex than in other isoforms. Identi fication of ESTs encoding TFIIS.h in mouse and human followed by the s equencing of cognate cDNA clones enabled the complete TFIIS.h coding r egion to be predicted. The conserved N- and C-terminal domains of mamm alian TFIIS.h (TCEA3) are separated by a linker region that is more va riable in sequence and that is also 50 amino acids longer than in othe r isoforms. The repetitive region of Xenopus TFIIS.h apparently corres ponds to an even more extended linker. Phylogenetic analysis of TFIIS sequences demonstrates the ancient origins of the three vertebrate iso forms, although they appeared functionally equivalent in in vitro RNA cleavage assays. (C) 1998 Academic Press.