A NUCLEAR MATRIX-ASSOCIATED HIGH-MOLECULAR-MASS NUCLEAR ANTIGEN, HMNA, OF CHICKEN AND MARKED DECREASE OF ITS IMMUNOREACTIVITY DURING THE PROGRESSION OF S-PHASE

A hnRNP-free nuclear matrix prepared from chicken MSB-1 cells was used to raise monoclonal antibodies,The monoclonal antibodies 2H3 and 3B7 showed identical nonhomogeneous immunofluorescence staining patterns o f nuclei in MSB-1 cells and chicken embryonic fibroblasts. In a synchr onized culture of MSB-1 cells, the immunoreactivity of nuclei with 2H3 , but not with 3B7, antibody decreased markedly during the progression of S phase, but returned to the normal level at the next G(1) phase, When cells were treated with Triton X-100 prior to fixation with paraf ormaldehyde or cells were fixed in methanol, nuclei were reactive with 2H3 antibody throughout the S phase, Both 2H3 and 3B7 antibodies reco gnized a high molecular mass nuclear antigen (HMNA) of approximately 5 50 kDa, which was associated with the nuclear matrix, HMNA was resista nt to extraction with 0.5 M NaCl from the nuclei at the G(1)/S boundar y but became extractable by the end of S phase, A cDNA clone, pBHB36, containing a partial sequence for HMNA was isolated by immunoscreening as a double positive clone with 2H3 and 3B7 antibodies, The deduced 1 ,150 residue-long sequence of pBHB36 shows no homology with any molecu les in the nucleotide and protein sequence databases, and contains dif ferent epitope regions for 2H3 and 3B7 antibodies, A possibility of hy drophobic association of HMNA with nuclear protein(s) during the progr ession of S phase is discussed.