To ensure proper quality of nuclear fractions, western blots with appropriate marker proteins were performed. Fraction 1 in both methods contains soluble, chromosomal proteins, released after DNaseI treatment, represented here by histone H2B. These proteins were washed out in subsequent steps of the preparation (fractions 2-3). The nuclear matrix fraction (fraction 4) was probed with a matrix-specific protein matrin 3 antibody (40) . Close association of Hax-1 with the nuclear matrix sheds new light on its mRNA-binding capacity and may indicate its role in regulation of transcript fate.