A chromosomal phosphoprotein is preferentially released by mild micrococcal-nuclease digestion

Immunological evidence for the role of phosphoprotein p68/pI = 7.3 in premessenger RNA splicing

A 68 kDa (pI = 7.3) nuclear phosphoprotein has been previously characterized as a component of transcriptionally active chromatin. Two-dimensional PAGE Western blotting and radioimmunoassay with monoclonal antibodies have identified this protein in nuclear extracts used for in vitro RNA splicing. In vitro splicing activity could be quantitatively inhibited by preincubating nuclear extracts with the antibodies, but the assembly of 60 S spliceosomes could not.

Characterization of the antigen reactive with anti-Scl-70 antibodies and its application in an enzyme-linked immunosorbent assay

The characteristics of the Scl-70 antigen (topoisomerase I) have been analyzed by means of autoantibodies. This antigen is a DNA-binding protein, dissociable from DNA at 0.3M NaCl and bound to a fraction of DNA that is very sensitive to nucleases. The molecular weight of the antigen is 105,000 daltons, whether dissociation conditions are used or not. Using chicken erythrocytes, and taking advantage of the strong interaction of the antigen with hydroxyapatite, we have designed a simple and fast purification protocol that allows the determination of anti-topoisomerase I antibodies by enzyme-linked immunosorbent assay.

Identification of a phosphoprotein in the nuclear matrix by monoclonal antibodies

Previous work in this laboratory has established that a rat liver nuclear phosphoprotein (B2:Mr 68,000, pI 6.5-8.2) is associated with actively transcribed nucleosomes, as demonstrated by its preferential release after mild treatment with micrococcal nuclease. In the present report we provide further immunological evidence ('Western Blot' analysis, solid-phase radioimmunoassay and indirect immunofluorescence) that in addition establishes the presence of this phosphoprotein in the nuclear-matrix protein fraction. This paradoxical localization suggests that this phosphoprotein may function in two separate and distinct roles within the realm of nuclear organization.

Monoclonal antibodies to a phosphoprotein from chromatin of rat liver

Three monoclonal antibody subclasses (IgG1, IgG2a, and IgM) were raised to the phosphoprotein B2 (Mr 68000, pI6.5-8.2) which has been shown previously to be associated with the nucleosomes of rat liver nuclei. These antibodies do not show any significant cross reactivity with CM-cellulose 'unbound' non-histone chromosomal proteins, bovine serum albumin or histones. Further verification of the specificity of these antibodies to this phosphoprotein was carried out using both 'dot' blot and immunological transfer analysis ('Western blot'). The monoclonal antibodies (IgG1 and IgG2a) could also be used to semi-quantify the phosphoprotein B2 in rat liver nuclei. The high specificity and unlimited availability of this type of probe provides a means to study the role(s) of this phosphoprotein in the overall scheme of actively transcribed chromatin.