A chromatin-associated protein from pea seeds preferentially binds histones H3 and H4

Pisum sativum p16 is a protein present in the chromatin of ungerminated embryonic axes. The purification of p16 and the isolation of a cDNA clone of psp54, the gene encoding its precursor have been recently reported [Castillo, J., Rodrigo, M. I., Márquez, J. A., Zúñiga, A and Franco, L. (2000) Eur. J. Biochem.267, 2156-2165]. In the present paper, we present data showing that p16 is a nuclear protein. First, after subcellular fractionation, p16 was clearly found in nuclei, although the protein is also present in other organelles. Immunocytochemical methods also confirm the above results. p16 seems to be firmly anchored to chromatin, as only extensive DNase I digestion of nuclei allows its release. Far Western and pull-down experiments demonstrate a strong in vitro interaction between p16 and histones, especially H3 and H4, suggesting that p16 is tethered to chromatin through histones. Because the psp54 gene is specifically expressed during the late development of seed, the role of p16 might be related to the changes that occur in chromatin during the processes of seed maturation and germination.