Trimethylation of histone H3 on lysine 4 (H3K4me3) localizes near the 5' region 
of genes and is tightly associated with active loci. Several proteins, such as 
CHD1, BPTF, JMJD2A, and the ING tumor suppressor family, directly recognize this 
lysine methyl mark. However, how H3K4me3 recognition participates in active 
transcription remains poorly characterized. Here we identify specific 
CHD1-interacting proteins via H3K4me3 affinity purification, including numerous 
factors mediating postinitiation events. Conventional biochemical purification 
revealed a stable complex between CHD1 and components of the spliceosome. 
Depletion of CHD1 in extracts dramatically reduced splicing efficiency in vitro, 
indicating a functional link between CHD1 and the spliceosome. Knockdown of CHD1 
and H3K4me3 levels by siRNA reduced association of U2 snRNP components with 
chromatin and, more importantly, altered the efficiency of pre-mRNA splicing on 
active genes in vivo. These findings suggest that methylated H3K4 serves to 
facilitate the competency of pre-mRNA maturation through the bridging of 
spliceosomal components to H3K4me3 via CHD1.