Cloning and Characterization of 5′-Upstream Sequence of the M32 Gene for a Mouse Homologue of Drosophila Heterochromatin Protein 1 (HP1)

M32 [also termed chromatin modifier protein 2 (MOD2)] is a nuclear protein consisting of the condensed chromatin structure (heterochromatin) and considered one of the mammalian homologues of heterochromatin protein 1 (HP1), first isolated as one of the components of heterochromatin in Drosophila. This report presents the isolation and characterization of the 5′-upstream region of the mouse M32 gene containing a promoter region and 5′-untranslated region (5′-UTR) exon. The 5′-upstream region (approximately 0.27 kb starting from the 5′ end of the 5′-UTR exon) of the M32 gene contained neither a TATA box nor a CCAAT box, but possessed potential binding sites for transcription factors such as Spl, H4TF-1, PEA2, PEA3, GSG element and Egr-1, and was highly G/C-rich. The promoter activity of this 5′-upstream region was demonstrated by transfecting its fusion-construct with the E. coli β-galactosidase gene into the F9 mouse teratocarcinoma cell line. The 5′ ends of the mRNA were mapped to at least two positions in the 5′-upstream region. Interestingly, the 5′-upstream region exhibited a high degree of similarity to a portion of heterogeneous nuclear ribonucleo-protein (hnRNP) A2/B1 gene, which is thought to play a role in RNA processing, located in the reverse orientation to the M32 gene, and also to several known ESTs and cDNAs. These findings suggest that the 5′-upstream region of the M32 gene consists of a multiple regulatory complex which probably plays important roles in nuclear function such as chromatin organization and RNA processing.