Processing and intracellular location of human astrovirus non-structural proteins

Human astrovirus (HAst) non-structural polyproteins are encoded in two open reading frames linked in expression by a ribosomal frameshifting event. Th e first of these (ORF 1a) specifies the serine protease, whilst the second (ORF Ib) encodes the virus RNA-dependent RNA polymerase. The ORF la product contains an unusual motif for small RNA viruses which could potentially di rect proteins to the cell nucleus. We have expressed part of ORF la contain ing this motif and the whole of ORF 1 b separately in recombinant baculovir us and raised specific antisera to each. We now report that expressed prote ins from ORF fa accumulate in the nucleus of both baculovirus-infected inse ct cells and HAst-infected CaCo-2 cells. In contrast the products of ORF Ib remain predominantly cytoplasmic.