Polyadenylation of histone H3 and H4 mRNAs in dicotyledonous plants

The histone H3 and H4 genes are shown to be expressed in both Arabidopsis plantlets and transitory multicellular suspension. The 5'- and 3'-ends of the H4 mRNAs have been localized on two H4 genes previously sequenced, H4A748 and H4A777. S1-nuclease mapping and reverse-transcriptase-primer-elongation experiments revealed the existence of two start points for transcription, located 31 and 37 nucleotides downstream from the TATA-box. The 3'-end of the mRNA corresponding to H4A748 was localized at 177 nt after the stop codon. The other gene, H4A777, most probably is not expressed. In addition to a long 3'-untranslated region, the H4 mRNA was shown to be polyadenylated in both plantlets and cell-suspension. This observation was extended to the H3 mRNAs of Arabidopsis and of two other dicots, tobacco and sunflower. Previous results on maize H3 and H4 mRNAs suggest that polyadenylation is a common feature for histone mRNAs in higher plants.