Characterization of the Nuclear Localization Signal of the Borna Disease Virus Polymerase

Borna disease virus (BDV) is a nonsegmented negative-strand RNA virus that replicates and transcribes its genome in the nucleus of infected cells. BDV proteins involved in replication and transcription must pass through the nuclear envelope to associate with the genomic viral RNA. The RNA-dependent RNA polymerase (L) of BDV is postulated to be the catalytic enzyme of replication and transcription. We demonstrated previously that BDV L localizes to the nucleus of BDV-infected cells and L-transfected cells. Nuclear localization of the protein presupposes the presence of a nuclear localization signal (NLS) within its primary amino acid sequence or cotransport to the nucleus with another karyophilic protein. Because L localized to the nucleus in the absence of other viral proteins, we investigated the possibility that L contains an NLS. The minimal sequence required for nuclear localization of L was identified by analyzing the subcellular distribution of deletion mutants of L fused to a flag epitope tag or β-galactosidase. Although the majority of the L fusion proteins localized to the cytoplasm of transfected BSR-T7 cells, a strong NLS (844RVVKLRIAP852) with basic and proline residues was identified. Mutation of this sequence resulted in cytoplasmic distribution of L, confirming that this sequence was necessary and sufficient to drive the nuclear localization of L

Absence of echovirus sequences in brain and spinal cord and amyotrophic lateral sclerosis patients

The role of enteroviruses in pathogenesis of amyotrophic lateral sclerosis (ALS) is controversial. A recent study, based on reverse transcription-polymerase chain reaction (RT-PCR) analysis of spinal cord, reported identification of a novel echovirus in 15 of 17 French subjects with ALS and only 1 of 29 subjects with other neurologic diseases. We established a real-time RT-PCR method based on this novel echovirus sequence and used this method and that previously employed for analysis of the French subjects to determine the prevalence of echoviral sequences in spinal cord and motor cortex of sporadic ALS subjects from the United States. No echoviral sequences were found in 20 spinal cord and 10 motor cortex samples from autopsy-confirmed cases of ALS or 13 spinal cord and 5 motor cortex samples from subjects with no motor neuron disease