Differential expression of the two types of histone H2A genes in wheat.

Five histone H2A cDNA clones have been isolated from a wheat cDNA library. They were divided into two groups, termed type 1 and type 2, based on their deduced amino acid sequences and their gene expression patterns. Three type 1 clones had ORFs encoding proteins similar to angiosperm histone H2As known so far, whereas two type 2 clones encoded an identical protein, which was more similar to Norway spruce (gymnosperm) H2A than to the angiosperm H2As. The C-terminus of the type 2 H2A was shorter than that of the type 1 H2As and lacked the characteristic SPKK motif that is conserved in angiosperm H2As. Northern analysis revealed that the mRNA levels of the type 1 H2A genes were high in proliferating cells during germination and in various tissues of young seedlings, while the mRNA levels of the type 2 genes were high in non-proliferating cells in which the type 1 gene was poorly expressed. This result suggests that the expression of these two groups of H2A genes is differently regulated during development in wheat.