Molecular cloning, sequence analysis and differential expression of an intron‐containing gene encoding tomato histone H1

Abstract

A tomato genomic clone has been identified which encodes histone H1. The deduced polypeptide is 287 amino acids in length, and exhibits the tripartite organization typical of histones H1. The central globular domain is highly similar to those regions from other H1 molecules, and the carboxyl-terminal domain contains a repeating hexapeptide motif, variants of which are conserved among H1 molecules. RNA gel blotting revealed that histone H1 mRNA is expressed at higher levels in organs which contain meristematic tissue and/or which have a high proportion of actively cycling cells. DNA gel blotting and dot-blot hybridization studies revealed that histone H1 in tomato is encoded by a small gene family. By employing the polymerase chain reaction on genomic DNA and on cDNA, it was determined that the gene is interrupted by an intron. The location and approximate length of the intron are conserved in both the tomato and Arubidopsis genes, with the intron separating the 'nose' region (encoded by exon 1) from the central globular domain (exon 2). The promoter region was found to contain several conserved sequence motifs which likely participate in the regulation of the gene.In most eukaryotic cells, the most elementary level of chromatin packaging is accomplished by the interaction of two molecules of each of the core histones H2A, H2B, H3 and H4 with 146-bp of duplex DNA to yield the core particle of the nucleosome. Adjacent core particles are connected by a linker DNA region of approximately 40-60 bp and, on average, there exists one molecule of histone Hlhucleosome. While the sequences of the core histones are well conserved between widely divergent species, histone H1 molecules exhibit striking sequence divergence. Despite this divergence, histone H1 molecules have maintained three distinct regions. These consist of an amino-terminal 'nose', a conserved central globular domain and a positively charged carboxy-terminal tail. One role of histone H1 is to act at a second level of the hierarchy of chromatin packaging to direct the formation and maintenance of the 30-nm chromatin fiber. It is generally thought that the positively charged lysine residues, found predominantly in the tail region, neutralize the negative phosphates of linker DNA to permit compaction of the chromatin fiber. Several lines of evidence suggest that the conserved central globular domain is responsible for sealing the points of entry and exit of DNA from the core particle [7]. In the central globular domain of histone H1 molecules from both plants and animals, there are many conserved resi-

Deletion of the unique gene encoding a typical histone H1 has no apparent phenotype in Aspergillus nidulans

“…No other gene encoding a linker histone is present in this organism. The A. nidulans coding sequence is shorter than animal (about 220 residues) and plant (240±274 residues) typical sequences (Gannt and Lenvik, 1991;Lindauer et al, 1993;Jayawardene and Riggs, 1994). The A. nidulans translated sequence lacks part of the amino terminus present in most histones of higher eukaryotes.…”

Endogenous cellulases in animals: Isolation of β-1,4-endoglucanase genes from two species of plant-parasitic cyst nematodes

“…In general, these Gly͞Ser-rich regions in proteins may allow flexibility between two functional domains (32). At the C-terminal extension of GR-ENG-2, a sequence [PAAAKK(S)PPAK] 3 was found with high similarity to parts of H1 histones of tomato involved in the protein-DNA interaction (33). Nematode EGases are functional outside the plant (1998) cell and it is hard to give a biological interpretation for this observation.…”

Structure and characterization of a putative drought-inducible H1 histone gene

“…One other tomato H1 histone has been described, tomH1B [24]. TomH1B, a cDNA isolated in a screen for meiotin-related genes, is quite different from Hisl.…”

“…This gene is only 70~o identical to His 1 and only over a 95 nucleotide stretch in the conserved central globular domain. [24], tobacco [37], pea [17], Arabidopsis [ 18], maize [32] and wheat [6]. proaches 75~o similarity to other plant H1 histones.…”

“…Outside of the central globular domain, these two H1 proteins do not share homology with one another or other H 1 proteins. A genomic sequence for a tomato HI histone has been reported [24] as well as several cDNA sequences: tobacco [37] pea [17] and maize [32].…”