Relatively little is known about the regulatory mechanisms of the Drosha/DGCR8 
complex, which processes miRNAs at the initial step of biogenesis. We found that 
histone deacetylase 1 (HDAC1) increases the expression levels of mature miRNAs 
despite repressing the transcription of host genes. HDAC1 is an integral 
component of the Drosha/DGCR8 complex and enhances miRNA processing by 
increasing the affinity of DGCR8 to primary miRNA transcripts via deacetylation 
of critical lysine residues in the RNA-binding domains of DGCR8. This finding 
suggests that HDACs have two arms for gene silencing: transcriptional repression 
by promoter histone deacetylation and post-transcriptional inhibition by 
increasing miRNA abundance.