ABSTRACT
Murine gammaherpesvirus 68 (MHV-68) infection of mice represents a viable small-animal model for the study of gammaherpesvirus pathogenesis. MHV-76 is a deletion mutant of MHV-68, which lacks four MHV-68-specific genes (M1 to M4) and eight viral tRNA-like sequences at the 5' end of the genome. These genes are implicated in latency and/or immune evasion. Consequently, MHV-76 is attenuated in the acute phase of in vivo infection with respect to MHV-68. Little is known about the role of M4 in viral infection, except that it is expressed as an immediate-early/early transcript during lytic replication of MHV-68 in vitro. To elucidate the contribution M4 makes to in vivo pathogenesis, we created a novel MHV-76 mutant (MHV-76inM4), in which the region of MHV-68 coding for M4 and accompanying putative promoter elements were inserted into the 5' region of the MHV-76 genome. The growth of MHV-76inM4 in vitro was indistinguishable from that of MHV-76 and MHV-68. However, virus titers from MHV-76inM4-infected BALB/c mice were significantly increased with respect to MHV-76 at early times in the lung. In addition, at days 17 and 21 postinfection, there was a significant elevation in latent viral load in splenocytes of MHV-76inM4-infected mice compared to MHV-76. Like MHV-76-infected mice, MHV-76inM4-infected mice display no evidence of overt splenomegaly, a finding characteristic of MHV-68 infection. M4 expression in vivo was detectable during productive infection in the lung and during the establishment of latency in the spleen, but in general M4 was not detectable during long-term latency (day 100 postinfection).
Subject(s)
Gammaherpesvirinae/pathogenicity , Gene Expression Regulation, Viral , Immediate-Early Proteins/genetics , Virus Activation , Virus Latency , Animals , Cell Line , Cricetinae , Female , Gammaherpesvirinae/genetics , Gammaherpesvirinae/physiology , Herpesviridae Infections/physiopathology , Herpesviridae Infections/virology , Immediate-Early Proteins/metabolism , Mice , Mice, Inbred BALB C , Transcription, Genetic , Virulence , Virus ReplicationABSTRACT
The Tn1546-related elements of 48 Van glycopetide-resistant enterococci were compared. Ten distinct Tn1546 types were identified with variation primarily due to IS1542 and IS1216V-like insertions. Clonal isolates frequently differed in their Tn1546 type, indicating instability of Tn1546-related elements. A putative hybrid promoter was identified, generated upstream of vanR by the insertion of IS1542. The presence of this hybrid promoter was associated with constitutive expression of the van genes and elevated teicoplanin resistance.
