The modular structure and function of the wheat H1 promoter with S phase-specific activity

Two histone H1 genes, TH315 and TH325, were isolated from a wheat genomic library. Nucleotide sequence analysis and comparison with other histone gene promoters revealed that the promoters of both genes contain many characteristic motifs conserved among plant histone H1 genes. They are 6 novel short stretches, named CS1 to CS6, and already documented elements or their relatives such as Oct, Oct-like (OLS), Nona-like (NonaLS), CCAAT box, and TATA box. Transient expression experiments with the TH315 promoter/GUS chimeric gene and its mutagenized derivatives showed that two Oct motifs, OLS, and CCAAT box are positive cis-acting elements. NonaLS and CS4 were suggested to be positive cis-acting elements and CS5 and CS6 to be negative elements. An Oct motif and CCAAT box constitutes a type III element and the 202-bp sequence containing these elements from -128 to +74 of the TH315 gene was shown to be sufficient to confer S phase-specific expression. The type III element is found in all plant histone H1 and H2B genes, suggesting that it is a subtype-specific element. Most plant histone genes have one of the type I, II, and III elements. We propose to classify the plant histone genes into three classes, based on the context of Oct in the promoters.