Structural organization and expression of the mouse gene for Pur‐1, 
a highly conserved homolog of the human MAZ gene

We have characterized the genomic structure and expression of the mouse gene for Pur‐1. The cloned Pur‐1 gene spans a 5‐kb region encompassing the promoter, five exons, four introns and the 3′‐untranslated region. All exon–intron junction sequences conform to the GT/AG rule. The promoter region has typical features of a housekeeping gene: a high G + C content (77.5%); a high frequency of CpG dinucleotides, in particular within the region 0.5 kb upstream of the site of initiation of translation; and the absence of canonical TATA and CAAT boxes. S1 nuclease protection assay demonstrated the presence of multiple sites for initiation of transcription around a site 108 nucleotides upstream of the ATG codon. Comparison of Pur‐1 with the human gene for MAZ (Myc‐associated zinc finger protein) revealed a striking homology of both their nucleotide and deduced protein sequences, an identical genomic organization and high similarity in promoter architecture and mRNA expression pattern. Sequence analysis of the 5′‐flanking region of Pur‐1 revealed numerous potential binding sites for transcription factors Sp1, AP‐2 and Pur‐1/MAZ itself. An element required for basal Pur‐1 expression was mapped from nucleotide – 258 to + 43. This region also mediated stimulation of basal transcription by ectopically expressed MAZ protein. We conclude that the Pur‐1 gene is the murine homolog of human MAZ and, like it, belongs to the family of housekeeping genes.