We have isolated a 1104 bp tobacco cDNA clone (H1c12) which includes a
n 846 bp open reading frame. This encodes a polypeptide of 282 amino a
cid residues and represents the largest plant Hi histone identified so
far. The structure of the deduced protein shows the classical tripart
ite organization of the H1-type linker histones. The expression of the
tobacco H1 histone gene(s) corresponding to the H1c12 cDNA clone was
examined during different developmental stages. We found that, al the
level of steady-state mRNA, expression of gene(s) encoding this H1 his
tone was rapidly induced in germinating seeds. The H1 gene was express
ed in all tissues examined. However, its expression tvas higher in tis
sues known to contain meristematic cells. Furthermore, in the leaves o
f mature plants accumulation of the H1 mRNA exhibits a very characteri
stic oscillation. This latter finding indicates that, at least in full
y developed plants, the expression of this type of H1 histone gene(s)
is modulated by a diurnal cycle.