Behavioural discrimination among chromosomal races of the house mouse (Mus musculus domesticus)

This work is concerned with the extent of behavioural discrimination between three chromosomal races of the house mouse (the standard 40-chromosome race and a 32- and 36-chromosome races) found in the vicinity of a hybrid zone in northern Scotland. Mice were investigated for several elements of their social behaviour. Within-population dyadic encounters did not show consistent behavioural differences attributable to karyotype among five populations (two standard race, two 36-chromosome race, one 32-chromosome race). Between-population dyadic encounters revealed significant differences between three populations. The standard population examined appeared to be the most “open” to foreigners, the 32-chromosome population the most “closed” while the 36-chromosome mice displayed an intermediate response. Differences in behaviour displayed during between-population as compared to within-population dyadic encounters revealed the occurrence of behavioural discrimination between populations. The implication of these results on the dynamics of the hybrid zone are discussed.     

Multiple topogenic sequences determine the transmembrane orientation of the hepatitis B surface antigen.

To investigate the mechanism by which complex membrane proteins achieve their correct transmembrane orientation, we examined in detail the hepatitis B surface antigen for sequences which determine its membrane topology. The results demonstrated the presence of at least two kinds of topogenic elements: an N-terminal uncleaved signal sequence and an internal element containing both signal and stop-transfer function. Fusion of reporter groups to either end of the protein suggested that both termini are translocated across the membrane bilayer. We propose that this topology is generated by the conjoint action of both elements and involves a specifically oriented membrane insertion event mediated by the internal sequence. The functional properties of each element can be instructively compared with those of simpler membrane proteins and may provide insight into the generation of other complex protein topologies.     

Closed circular viral DNA and asymmetrical heterogeneous forms in livers from animals infected with ground squirrel hepatitis virus

To identify possible intermediates in the replication of ground squirrel hepatitis virus, we characterized the major forms of intracellular virus-specific DNA in the livers of infected ground squirrels. A variety of DNA species were found: covalently closed circular molecules, relaxed circular molecules, and a heterogeneous collection of molecules that migrated ahead of closed circular DNA during agarose gel electrophoresis. The heterogeneous DNA was at least partly single stranded, consisted of minus strands in a greater than eight-fold mass excess of plus strands, and was tightly associated with protein.     

Apoptosis is induced by N-myc expression in hepatocytes, a frequent event in hepadnavirus oncogenesis, and is blocked by insulin-like growth factor II.

Induction of hepatocellular carcinoma in woodchucks by woodchuck hepatitis virus is associated with the activation of N-myc gene expression, usually by viral DNA integration in cis to the N-myc locus. We have examined the consequences of N-myc up-regulation in rodent hepatic cells in culture. Mouse alpha ML hepatocytes infected with a retroviral vector overexpressing the woodchuck N-myc2 gene display a higher proliferation rate than parental alpha ML cells but are morphologically unchanged and do not form colonies in soft agar. However, they display an increased propensity to undergo apoptosis, an effect that is markedly augmented by serum deprivation. Expression of the woodchuck hepatitis virus X gene in alpha ML cells does not alter the growth phenotype of the cells and has no effect upon N-myc-dependent apoptosis. However, apoptosis in N-myc2-expressing alpha ML cells is strongly inhibited by insulin-like growth factor II (IGF II). IGF II gene expression is also strongly up-regulated during hepatic carcinogenesis in vivo in virally infected animals and has been speculated to be part of an autocrine growth-stimulatory pathway. Our results suggest that IGF II may play another role in the development of virus-induced hepatoma: the prevention of programmed cell death triggered by deregulated N-myc expression.     

The size and conformation of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) DNA in infected cells and virions.

The genome of a novel human herpesvirus has been detected in specimens of Kaposi's sarcoma (KS) and in several AIDS-related lymphoproliferative disorders. Here we examine the size and genomic conformation of the DNA of this virus (known as KS-associated herpesvirus or human herpesvirus 8) in latently and lytically infected cells and in virions. Pulsed-field gel electrophoresis of viral DNA shows that the viral genome is similar in size to those of other gammaherpesviruses (160 to 170 kb). As with Epstein-Barr virus, KS-associated herpesvirus DNA is stably maintained in latently infected B cells as episomal monomer circles and induction from latency is associated with the selective accumulation of linear genomic forms.     

Effects of mutations within and adjacent to the terminal repeats of hepatitis B virus pregenomic RNA on viral DNA synthesis.

The viral polymerase and several cis-acting sequences are essential for hepadnaviral DNA replication, but additional host factors are likely to be involved in this process. We previously identified two sequences, UBS and DBS (upstream and downstream binding sites), present in multiple copies in and adjacent to the pregenomic RNA (pgRNA) terminal redundancy, that were specifically recognized by a 65-kDa host factor, p65. The possible roles of these two sequences in hepatitis B virus (HBV) replication were investigated in the context of the intact viral genome. UBS is contained within the terminal redundancy of pgRNA, and the 5' copy of this sequence is essential for viral replication. Mutations within the central core of UBS ablate p65 binding and selectively block synthesis of plus-strand DNA, without affecting RNA packaging or minus-strand synthesis. The DBS sequence, which is located downstream of the pgRNA polyadenylation site, overlaps the core (C) protein coding region. All mutations introduced into this site severely affected viral replication. However, these effects were shown to result from dominant negative effects of mutant core polypeptides rather than from cis-acting effects on RNA recognition. Thus, the 5' UBS but not DBS sites play important cis-acting roles in HBV DNA replication; however, the involvement of p65 in these roles remains a matter for investigation.