Cloning and structural analysis of cDNA and the gene for mouse transcription factor UBF

The gene and protein structure of the mouse UBF (mUBF), a transcription factor for mouse ribosomal RNA gene, have been determined by cDNA and genomic clones. The unique mUBF gene consists of 21 exons spanning over 13 kb. Two mRNAs coding for mUBF1 and mUBF2 having 765 a.a. and 728 a.a., respectively, are produced by an alternative splicing of exon 8. It specifies 37 amino acids constituting a part of the regions homologous to high mobility group proteins (HMG box 2). A human UBF (hUBF) cDNA obtained by polymerase chain reaction also indicates the presence of two kinds of mRNAs, the shorter form lacking the same region as mUBF2. Comparison of the cDNAs from hUBF and mUBF revealed an unusual conservation of nucleotide sequence in the 3'-terminal non-coding region. We examined the relative amounts of expression of mUBF1 and mUBF2. The eight tissues studied contained both molecular species, although mUBF2 was the predominant form of UBF. The mRNA of mUBF1 was expressed one half of the mUBF2 in quiescent mouse fibroblasts but reached the same amount in growing state.