A zinc finger-containing papain-like protease couples subgenomic mRNA synthesis to genome translation in a positive-stranded RNA virus

The genome expression of positive-stranded RNA viruses starts with translation rather than transcription. For some viruses, the genome is the only viral mRNA and expression is regulated primarily at the translational level and by limited proteolysis of polyproteins. Other virus groups also generate subgenomic mRNAs later in the reproductive cycle. For nidoviruses, subgenomic mRNA synthesis (transcription) is discontinuous and yields a 5′ and 3′ coterminal nested set of mRNAs. Nidovirus transcription is not essential for genome replication, which relies on the autoprocessing products of two replicase polyproteins that are translated from the genome. We now show that the N-terminal replicase subunit, nonstructural protein 1 (nsp1), of the nidovirus equine arteritis virus is in fact dispensable for replication but crucial for transcription, thereby coupling replicase expression and subgenomic mRNA synthesis in an unprecedented manner. Nsp1 is composed of two papain-like protease domains and a predicted N-terminal zinc finger, which was implicated in transcription by site-directed mutagenesis. The structural integrity of nsp1 is essential, suggesting that the protease domains form a platform for the zinc finger to operate in transcription.

Hepatic expression of mature transforming growth factor beta 1 in transgenic mice results in multiple tissue lesions.

Aberrant expression of transforming growth factor beta 1 (TGF-beta 1) has been implicated in a number of disease processes, particularly those involving fibrotic and inflammatory lesions. To determine the in vivo effects of overexpression of TGF-beta 1 on the function and structure of hepatic as well as extrahepatic tissues, transgenic mice were generated containing a fusion gene (Alb/TGF-beta 1) consisting of modified porcine TGF-beta 1 cDNA under the control of the regulatory elements of the mouse albumin gene. Five transgenic lines were developed, all of which expressed the Alb/TGF-beta 1 transgene selectively in hepatocytes. The transgenic line 25 expressing the highest level of the transgene in the liver also had high (> 10-fold over control) plasma levels of TGF-beta 1. Hepatic fibrosis and apoptotic death of hepatocytes developed in all the transgenic lines but was more pronounced in line 25. The fibrotic process was characterized by deposition of collagen around individual hepatocytes and within the space of Disse in a radiating linear pattern. Several extrahepatic lesions developed in line 25, including glomerulonephritis and renal failure, arteritis and myocarditis, as well as atrophic changes in pancreas and testis. The results from this transgenic model strongly support the proposed etiological role for TGF-beta 1 in a variety of fibrotic and inflammatory disorders. The transgenic model may also provide an appropriate paradigm for testing therapeutic interventions aimed at neutralizing the detrimental effects of this important cytokine.