A functional interaction between the survival motor neuron complex and RNApolymerase II

The survival motor neuron (SMN) protein, the protein product of the spinal muscular atrophy (SMA) disease gene, plays a role in the assembly and regen eration of small nuclear ribonucleoproteins (snRNPs) and spliceosomes. By n anoelectrospray mass spectrometry, we identified RNA helicase A (RHA) as an SMN complex-associated protein. RHA is a DEAH box RNA helicase which binds RNA polymerase II (pol II) and reportedly functions in transcription. SMN interacts with RHA in vitro, and this interaction is impaired in mutant SMN s found in SMA patients. Coimmunoprecipitation demonstrated that the SMN co mplex is associated with pol II, snRNPs, and RHA in vivo. In vitro experime nts suggestthat RHA mediates the association of SMN with the COOH-terminal domain of pol II. Moreover, transfection of cells with a dominant negative mutant of SMN, SMN Delta N27, causes accumulation of pol II, snRNPs, and RH A in nuclear structures that contain the known markers of gems and coiled b odies, and inhibits RNA pol I and pol II transcription in vivo. These findi ngs indicate a functional as well as physical association of the SMN comple x with pol II and suggest a role for the SMN complex in the assembly of the pol II transcription/processing machinery.