Abstract
Mammalian HMGI proteins belong to the high mobility group (HMG) of small non-histone nuclear proteins, and function as architectural factors to mediate structural changes in DNA. The HMGI family consists of three members: HMGI, HMGY and HMGI-C. As pseudogenes have complicated the genomic analysis of murine
Hmgi(y), a mouse lambda FIX II genomic library was screened with an intron-specific probe to identify and characterize the authentic
Hmgi(y) gene. The murine
Hmgi(y) gene is 7.2
kb long and contains four protein coding exons and two additional exons encoding part of the 5′ untranslated region. Sequencing confirms that an alternative splicing site within exon 3 results in the two protein isoforms: Hmgi and Hmgy. Primer extension experiments revealed that at least three transcription start sites exist in the 5′ end of the gene. It has been well established that the expression of both
Hmgi-c and
Hmgi(y) is readily detectable throughout embryogenesis. Unlike
Hmgi-c, whose expression is restricted to embryogenesis, a Northern hybridization analysis showed low-level expression of
Hmgi(y) in adult mouse tissues. Similarly, when tissues from newborn animals were examined,
Hmgi(y) expression was readily detected at a level of intensity intermediate between that found in embryos and adults. Understanding the gene structure and expression pattern will provide important insights into the in-vivo function of
Hmgi(y).