Peptide sequence analysis of two newly identified members of the murine "High Mobility Group" of nonhistone chromatin proteins, HMG-I and HMG-Y, revealed that these proteins are identical (except for an internal deletion of 11 residues in the HMG-Y protein) and each contains two exact copies of a conserved palindromic amino acid sequence motif whose structure is similar to the DNA-binding, antitumor and antiviral, peptide drugs distamycin and netropsin. Pure HMG-I or HMG-Y proteins specifically bind, in vitro, to stretches of A/T-rich DNA found in the flanking regulatory regions of many areas of mammalian chromosomes including G/O bands, centromeres and telomeres in vivo. Nucleotide sequence analyses of the cDNA clones coding for these isoform protiens indicate that they are derived from a common mRNA precursor by alternative splicing. Therefore, the following specific research aims are proposed: (i) Determine which regions of these isoform proteins are responsible for specific DNA binding and determine whether there are differences between HMG-I and HMG-Y in their association with A/T rich sequences of DNA; (ii) Utilizing synchronized cells, investigate HMG-I and HMG-Y protein synthesis and mRNA synthesis and splicing during different phases of the cell cycle; (iii) Utilizing synchronized cells, investigate possible differences in the distribution of the HMG-I and HMG-Y proteins between the nucleus and cytoplasm during different phases of the cell cycle. (iv) Investigate possible differences in chromosomal localization of the HMG-I and HMG-Y proteins on mitotic chromosomes. The results of these experiments may provide important clues to the biological function of these proteins.
