Structure, chromosomal localisation and expression of the murine dominant negative helix-loop-helix Id4 gene

Id proteins antagonise the functional properties of DNA-binding, basic helix-loop-helix transcription factors. Id proteins inhibited cell differentiation in various model systems, both in vitro and in vivo. They are transcriptionally and post-transcriptionally regulated during cell cycle progression and promote cell proliferation. In order to establish the molecular and functional properties of Id4, we analysed structure, chromosomal localisation and expression of the murine Id4 gene. Sequence analysis indicated that the Id4 gene consists of three exons. Multiple transcription start sites map about 300 bp upstream of the ATG translational start codon within a 30-bp region of the Id4 promoter, which lacks a classic TATA box. Expression of the Id4 gene results in four major transcripts, most likely generated by differential use of polyadenylation sites. Abundance of the four transcripts varies across tissues, suggesting tissue-specific regulation of polyadenylation and/or post-transcriptional regulation of Id4 expression. However, the Id4 gene seems to be expressed as a single protein. Id4 expression is switched on during embryogenesis between day 7.5 and 9.5 of gestation and is most abundant in adult brain, kidney and testis. Id4 maps to chromosome 13 of the mouse.