Tightly bound matrix DNA probably plays an important role in organization of chromosome centromeres

A large variety of DNA sequences have been described in matrix attachment regions (MARs), This is a result of the different methods used for their isolation. Here we used the conventional procedure for preparing nuclear matrix from Friend-S cells and found that the fibrogranular network of the matrix is formed by uniform-looking tightly packed granules. The residual DNA extracted from matrix is enriched in highly repetitive sequences. Our previous investigations indicated that these MARs-DNA are probably constitutive in the cell cycle. The DNA was partially cloned to obtain additional information about the nature of these sequences, In sits hybridization with cloned DNAs showed that the formation of clusters in interphase nuclei is a result of close disposition of the centromeric regions of a few chromosomes, Computer analysis of the sequences of two MARs did not reveal any significant homologies with the known sequences in the NCBI database. The comparison of other two clones showed a high degree of similarity to mouse repetitive families, In one of the clones we found four TGGAA motifs which could nucleate stem-loop structures. This unusual structure could explain the unique morphology and function of the mouse centromere in mitosis.