A novel histone variant localized in nucleoli of higher plant cells

Immunofluorescence staining with antisera raised against p35, a basic nucle ar protein that accumulates in the pollen nuclei of Lilium longiflorum, spe cifically stained the nucleoli in interphase nuclei of somatic tissues, inc luding root and leaf, and in pachytene nuclei during meiotic division, wher eas antisera raised against histone H1 uniformly stained the entire chromat in domain with the exception of the nucleoli in these nuclei. Further, p35- specific antisera stained the nucleoli in root and leaf nuclei of the monoc otyledonous plants Tulipa gesneriana. Allium cepa and Triticum aestivum and of the dicotyledonous plants Vicia faba and Nicotiana tabacum. Thus, these novel antisera stained the nucleoli in cells of all higher plants examined , although the staining patterns within nucleoli were somewhat different am ong plant species and tissues. The full-length cDNA of p35 was cloned on th e basis of the partial amino acid sequence. The deduced amino acid composit ion and amino acid sequence of p35 indicate that this nucleolar protein is a novel variant of histone I-Il. Further, p35 was strongly bound to ribosom al DNA in vitro. The results of immunoblotting of histones extracted from e ach tissue of the various plant species with the nucleolus-specific antibod ies also suggested the conservation of similar epitope(s) in both mono- and dicotyledonous plants. From these results, it is suggested that similar va riants of histone H1 an specifically distributed in the nucleoli of all pla nt species and help to organize the nucleolar chromatin.