A pea nuclear protein that is induced by dehydration belongs to the vicilin superfamily

The purification to homogeneity of p16, a protein with an electrophoretic m obility compatible with an apparent molecular mass of 16 kDa, from nuclei o f ungerminated pea embryonic axes is described. A cDNA clone of its gene, w hich was designated psp54, was also isolated. The psp54 cDNA contains an op en reading frame coding for a 54.4-kDa polypeptide (p54). p16 corresponds t o the C-terminal third of p54, although the mechanisms by which the primary polypeptide could be processed are not yet known. The sequence of p54 is 6 0% identical with that of the precursor of a sucrose-binding soybean protei n, and, to a lesser extent (31-34%), it shares homology with some storage p roteins. p16 is also 30% homologous with Nhp2p, a yeast nuclear protein. Th e psp54 gene, present in a single copy in pea genome, starts being expresse d during seed desiccation. Soon after rehydration in seed germination, p54 mRNA disappears and is no longer detectable in vegetative tissues, except i n response to hydric stress (exposure to abscisic acid, osmolites or desicc ation). p16 can be recovered from nuclei cross-linked to histone H3, when t he disulfide bridges that occur in vivo are preserved. On the other hand, p 16 shares some properties with dehydrins, which are thought to protect cell ular structures against desiccation. We propose that the possible precursor polypeptide p54 belongs to the vicilin superfamily, members of which play a variety of roles. The function of p16 may be related to the protection of chromatin structure against desiccation during seed development.