The coronavirus mouse hepatitis virus (MHV) translates its replicase gene (gene 1) into two co-amino-terminal polyproteins, polyprotein 1a and polyprotein 1ab. The gene 1 polyproteins are processed by viral proteinases to yield at least 15 mature products, including a putative RNA helicase from polyprotein 1ab that is presumed to be involved in viral RNA synthesis. Antibodies directed against polypeptides encoded by open reading frame 1b were used to characterize the expression and processing of the MHV helicase and to define the relationship of helicase to the viral nucleocapsid protein (N) and to sites of viral RNA synthesis in MHV-infected cells. The antihelicase antibodies detected a 67-kDa protein in MHV-infected cells that was translated and processed throughout the virus life cycle. Processing of the 67-kDa helicase from polyprotein 1ab was abolished by E64d, a known inhibitor of the MHV 3C-like proteinase. When infected cells were probed for helicase by immunofluorescence laser confocal microscopy, the protein was detected in patterns that varied from punctate perinuclear complexes to large structures that occupied much of the cell cytoplasm. Dual-labeling studies of infected cells for helicase and bromo-UTP-labeled RNA demonstrated that the vast majority of helicase-containing complexes were active in viral RNA synthesis. Dual-labeling studies for helicase and the MHV N protein showed that the two proteins almost completely colocalized, indicating that N was associated with the helicase-containing complexes. This study demonstrates that the putative RNA helicase is closely associated with MHV RNA synthesis and suggests that complexes containing helicase, N, and new viral RNA are the viral replication complexes.

We report the characterization of three UBA2 genes (UBA2a, -b, and -c; corresponding to At3g56860, At2g41060, and At3g15010) encoding Arabidopsis thaliana proteins with high homology to Vicia faba AKIP1 and other heterogeneous nuclear ribonucleoprotein (hnRNP)-type RNA-binding proteins. In vitro RNA binding assays revealed that the three UBA2 proteins interact efficiently with homoribopolymers. Biolistic transient expression of UBA2-GFPs demonstrated that the three UBA2 proteins localize to the nucleus. Expression analysis by RNA gel blot, RT-PCR, and promoter::GUS assays showed that UBA2 transcripts are present in all organs. UBA2 genes are subject to alternative splicing affecting only the 3'-untranslated regions (UTRs): six different splice variants were detected for UBA2a, and two each were found for UBA2b and UBA2c. RT-PCR and quantitative real-time RT-PCR analysis showed that the levels of UBA2 transcripts are regulated by wounding in a splice variant-specific manner: splice variants UBA2a.1 and UBA2c.1 increased following mechanical wounding. Wounding effects on gene expression are transduced by methyl jasmonate (MeJA)-dependent and oligogalacturonide (OGA)-dependent pathways. However, neither MeJA nor OGA treatment altered levels of any of the UBA2 transcripts, and other plant hormones implicated in wound responses, ethylene and abscisic acid (ABA), also had no effect on accumulation of UBA2 transcripts. Taken together, these results imply that the three UBA2 genes encode hnRNP-type nuclear RNA-binding proteins that function in a novel wound signal transduction pathway.

In this study, we investigated the relationship between reovirus-induced apoptosis and viral growth. Madin-Darby canine kidney (MDCK) epithelial cells infected with prototype reovirus strains type 1 Lang (T1L) or type 3 Dearing (T3D) were found to undergo apoptosis, and T3D induced apoptosis of MDCK cells to a substantially greater extent than T1L. By using T1L ؋ T3D reassortant viruses, we found that differences in the capacities of these strains to induce apoptosis are determined by the viral S1 and M2 gene segments. These genes encode viral outer-capsid proteins that play important roles in viral entry into cells. T1L grew significantly better in MDCK cells than T3D, and these differences in growth segregated with the viral L1 and M1 gene segments. The L1 and M1 genes encode viral core proteins involved in viral RNA synthesis. Bcl-2 overexpression in MDCK cells inhibited reovirus-induced apoptosis but did not substantially affect reovirus growth. These findings indicate that differences in the capacities of reovirus strains to induce apoptosis and grow in MDCK cells are determined by different viral genes and that premature cell death by apoptosis does not limit reovirus growth in MDCK cells.

Concentrations of IGF-I and IGF-II, and IGF binding proteins (IGFBP) in serum and mammary gland secretions were surveyed during the dry period and early lactation of 30 Holstein cows. Although there was a threefold drop in the concentration of IGF-I in serum from the last week of the dry period to parturition (81 +/- 7 to 24 +/- 3 ng/ml, P less than .01), there was no significant change in serum IGF-II concentration during this period (150 +/- 17 vs 173 +/- 13 ng/ml, P greater than .05). Furthermore, a 57% increase in serum IGF-I was observed from the last week of lactation to the second week of drying off (100 +/- 5 to 157 +/- 8 ng/ml, P less than .05). Changes in serum IGF-II were not observed (126 +/- 11 vs 150 +/- 10 ng/ml, respectively; P greater than .05). Although IGF-I, IGF-II, and IGFBP concentrations in mammary secretions peaked 2 wk before parturition (2.95 +/- 1.1, 1.83 +/- .6, and 7.27 +/- .76 micrograms/ml, respectively), total output/quarter was highest in colostrum (394 +/- 119, 295 +/- 132, and 2,680 +/- 1,967 micrograms/quarter, respectively). Weekly milking of two individual quarters during the dry period did not affect (P greater than .05) IGF-I or IGF-II concentration (ng/ml) or total output (microgram/quarter) and milk yield in colostrum and milk (2 wk and 7 wk) compared with the ipsilateral quarter. The data support the hypothesis that IGF-I may be transported by the mammary gland epithelium. Furthermore, the secretion mechanisms of IGF-I, IGF-II, and IGFBP by the gland may be related to each other.

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