Mammalian metaphase chromosomes can be identified by their characteristic banding pattern when stained with Giemsa dye after brief proteolytic digestion. The resulting G-bands are known to contain regions of DNA enriched in A/T residues and to be the principal location for the L1 (or Kpn 1) family of long interspersed repetitive sequences in human chromosomes. Here we report that antibodies raised against a highly purified and biochemically well characterized nonhistone "High-Mobility Group" protein, HMG-I, specifically localize this protein to the G-bands in mammalian metaphase chromosomes. In some preparations in which chromosomes are highly condensed, HMG-I appears to be located at the centromere and/or telomere regions of mammalian chromosomes as well. To our knowledge, this is the first well-characterized mammalian protein that localizes primarily to G-band regions of chromosomes.

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