High mobility group (HMG) proteins are abundant non-histone proteins of the eukaryotic chromatin with assumed functions in chromatin structure and its regulated expression. In maize, four different HMG proteins (a, b, c and d) have been identified. In the case of the HMG-box containing HMGa protein, studies have so far been performed with a cloned cDNA (Grasser and Feix, Nucl. Acids Res. 19:2573-2577, 1991) and with isolated and recombinant proteins (Grasser et al., Plant J. 6:351-358, 1994). Our current work on the genomic organization of HMG coding sequences (working with Southern analysis and cloned genomic fragments) revealed that several HMG protein coding sequences (complete and fragments) are scattered in the genome. In addition to the gene (consisting in the coding region of seven exons) three separate single exon containing fragments and a complete retro-pseudogene have been identified. This finding reminds us of the results obtained with the human HMG system (Stros and Dixon, Biochim. Biophys. Acta 1172:231-235, 1993). Our current picture of the HMGa gene system is summarized in the scheme on the following page.

The HMGa gene and the fragments GEXON2 and GEXON6 were obtained by screening genomic libraries prepared from maize line A619. The structure of ZMHMG was taken from the literature (Yanagisawa and Izui, Plant Mol. Biol. 23:915, 1993). The retropseudogene was obtained by PCR amplifications from DNAs of different maize lines including A619. The cDNA was previously isolated from a cDNA library (Grasser and Feix, 1991). The -helices I, II and III are part of the HMG-box DNA binding domain. 

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