Reproductive toxicology. m-/p-cresol.

Like the major vaccinia virus (VV) core protein precursors, p4b and p25K, the 25 kDa VV A12L late gene product (p17K) is proteolytically maturated at the conserved Ala-Gly-Ala motif. However, the association of the precursor and its cleavage product with the core of mature virion suggests that both of the A12L proteins may be required for virus assembly. Here, in order to test the requirement of the A12L protein and its proteolysis in viral replication, a conditional lethal mutant virus (vvtetOA12L) was constructed to regulate A12L expression by the presence or absence of an inducer, tetracycline. In the absence of tetracycline, replication of vvtetOA12L was inhibited by 80% and this inhibition could be overcome by transient expression of the wild-type copy of the A12L gene. In contrast, mutation of the AG/A site abrogated the ability of the transfected A12L gene to rescue, indicating that A12L proteolysis plays an important role in viral replication. Electron microscopy analysis of the A12L deficient virus demonstrated the aberrant virus particles, which were displayed by the AG/A site mutation. Thus, we concluded that the not only A12L protein but also its cleavage processing plays an essential role in virus morphogenic transition. Background Proteolytic processing in vaccinia virus (VV) plays an important role in morphogenic transitions during the virus replication cycle. To date, six VV-encoded, proteolytically processed proteins have been reported. They are the gene products of A10L (p4a), A3L (p4b), L4R (p25K), A17L (p21K), G7L, and A12L (p17K) [1-6]. Extensive studies of these proteins have provided more specific mechanisms of VV proteolysis in terms of the transformation of immature virions (IV) into intracellular mature virions (IMV). One of the VV major core proteins, A10L has been shown to be essential in virus replication and its absence in virus assembly resulted in defective virus morphology such as IV-like particles, which lacked granular viral materials and consequently produced the irregular-shaped virus particles [7]. These morphogenic defects suggested that A10L protein is required for the correct organization of the nucleocomplex within the IVs [7,8]. L4R, a DNA binding protein, plays an essential role in virus replication, being involved in an early stage of infection such as early transcription or unpackaging viral core and DNA [9,10]. The L4R-deficient virus produced virus particles with nonassociated viroplasm and its surrounding viral membranes, suggesting its role in correct incorporation of viral DNA and cores with immature virus membrane. Published: 11 July 2007 Virology Journal 2007, 4:73 doi:10.1186/1743-422X-4-73 Received: 29 June 2007 Accepted: 11 July 2007 This article is available from: http://www.virologyj.com/content/4/1/73 © 2007 Yang and Hruby; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.