A monoclonal antibody (HO-No-1) with specificity for a human nucleolar protein

A murine monoclonal antibody (named HO-No-1) which specifically reacts with a target antigen of 72,000 mol. wt (p72) in the nucleoli of human cells, has been isolated. Using an avidin-biotin peroxidase immunoperoxidase method, it was found that this antibody stains exclusively the nucleolus and not other portions of the nucleus and cytoplasm. This reaction pattern was observed consistently, although to different degrees in 14 human normal tissues and human malignant cell lines. However, after pretreatment with actinomycin D (250 ng/ml) for 2 h, the antibody stains the nucleoplasm uniformly. Thus this study demonstrates evidence for an antibody which reacts specifically with human nucleoli to a protein which could play an important role in rRNA synthesis.