Posttranslational Modifications of Histones by Methylation

Abstract

This chapter demonstrates that an RNA polymerase II elongation factor—the Paf1 complex—is required for the recruitment of histone methyltransferases to the elongating RNA polymerase and suggests that it is possible that modification by methylation may serve as a mark of transcriptional memory for transcribed genes. Histone modifications by methylation are demonstrated to play a pivotal role in the regulation of chromatin dynamics and gene expression. Several proteins to date have been identified as functioning as histone methyltransferases with different substrate specificity. The wealth of other uncharacterized SET domain containing proteins in the database has set the stage for characterization of the role of such enzymes. To date, two types of histone methylation have been observed—methylation of the ɛ-amino group of lysine and methylation of the Nη nitrogen of the arginine side chain guanido group. The first histone methyltransferase to be identified was the product of the drosophila suppressor of position-effect variegation gene. Since its initial discovery, the SET domain has been described as a part of several proteins involved in modulating gene activity in eukaryotes ranging from yeast to humans. The methylation of arginine residues of histone proteins has also received much attention in recent years. However, not much is known about the biological significance of this process as of yet. Recent experiments have identified three distinct types of methylation that occur at arginine residues on histone tails along with two types of PRMTs that accomplish this task.