Nuclear matrix proteins (with molecular masses of 38 and 50 kDa) are transported by chromosomes in mitosis

Abstract

Using the immunofluorescence method, sera M-68 and K-43 from patients with autoimmune diseases were shown to stain interphase nuclei and the periphery of mitotic chromosomes of pig embryo kidney cells. Western blotting revealed a polypeptide with a molecular mass of 50 kDa in M-68 serum and polypeptide with a molecular mass 38 kDa in K-43 serum. In the nuclear protein matrix, the antibodies to protein with a molecular mass of 38 kDa stained only the nucleolar periphery, while the antibodies to protein with a molecular mass of 50 kDa stained not only the nucleolar periphery, but also all interphase nuclei. It was shown that, among all components of the nuclear protein matrix (lamina, internuclear network, residual nucleoli), only the nucleolar periphery contained the 38-kDa protein, while the 50-kDa protein was part of the residual nucleolar periphery and participated in the formation of a nuclear-protein network. Both proteins in interphase cell in situ were located in nuclei, but one of them with a molecular mass of 50 kDa was in the form of small, clearly outlined granules, while the other protein (38 kDa) was in the form of small, bright granules on a background of a diffusely stained nucleus. Both proteins also were revealed as a continuous rim around the nucleolar periphery. During all mitotic stages, the 50-kDa protein was seen over the whole chromosomal periphery as a sheath, while the 38-kDa protein formed individual fragments and granules around them. After the decondensation of the nucleus and chromosomes induced by hypotonic treatment, both antibodies stained interphase nuclei diffusely, whereas, in mitotic cells, they stained the surfaces of swollen chromosomes. Polypeptide with a molecular mass of 50 kDa maintained a strong connection with the periphery of the chromosome in the norm during decondensation induced by hypotonic treatment and during subsequent recondensation in isotonic medium, while, during recondensation, protein with a molecular mass of 38 kDa partially lost contact with the chromosome and, at the same time, appeared in the form of granules in the cytoplasm. The obtained data allow one to conclude that nuclear matrix proteins can be transferred with peripheral chromosomal material; similar to the main nucleolar proteins (fibrillarin, B-23, nucleolin, et al.) and some non-nucleolar components of the nuclear protein matrix, they can also have connections of different stabilities with chromosomal periphery.