FIGURE 3.

Human Suv4-20 proteins also mediate formation of 2mK20-H4 in vivo. Typical results are shown for days 4 and 8 of treatment of HeLa cells with siRNA targeting firefly luciferase (negative control) or pooled siRNA targeting both Suv4-20h1 and Suv4-20h2. A, relative levels of mRNA for Suv4-20h1 and Suv4-20h2 detected by RT-PCR. The levels of actin mRNA were used to ensure equivalent loading. B, relative levels of 1m, 2m, and 3mK20-H4 detected by immunoblotting with H4 Lys-20 methylation state-specific antisera. The levels of α-tubulin were used to ensure equivalent loading. C, Fourier transform mass spectra of H4 from siRNA-treated cells. Slightly different amounts of sample were analyzed in each case, so the spectra are normalized according to the height of the tallest peak.