Functional characterization of the Drosophila Hmt4-20/Suv4-20 histone methyltransferase

Abstract

Di- and trimethylation of histone H4 lysine20 (H4K20) are thought to play an important role in controlling gene expression in vertebrates and in Drosophila. By inducing a null mutation in Drosophila Suv4-20, we show that it encodes the histone H4 lysine20 di- and trimethyltransferase. In Suv4-20 mutants, the H4K20 di- and trimethyl marks are strongly reduced or absent, and the monomethyl mark is significantly increased. We find that even with this biochemical function, Suv4-20 is not required for survival and does not control position-effect variegation (PEV).

Figure 1.—

The Suv4-20-skpA genomic region. Three P-element insertions in the Suv4-20 gene; the two newly isolated deletions and the primers (arrows) used in the RT–PCR experiments are indicated.

Figure 2.—

Suv4-20 is the di- and trimethyltransferase of histone H4K20. (A) RT–PCR experiment of RNA isolated from hemizygous Df(1)174 and Df(1)109 larvae. Only the skpA mRNA is absent in Df(1)174. (B) Western blots of wild-type and Df(1)109; P{w⁺, skpA} double-homozygous larvae. The monomethyl mark is increased in the deficiency animals, while the H4K20 me2 and me3 marks are strongly reduced or absent.

Figure 3.—

The H4K20 di- and trimethyl mark is not detected on Df(1)109/Y salivary gland chromosomes. Wild type (left) and mutant salivary gland chromosomes, stained with anti-dimethylated and anti-trimethylated H4K20 antibody (red), are indicated. DNA was stained with Hoechst (blue).