The inverse relationship between chronic HBV and HCV infections among injection drug users is associated with decades of age and drug use.

Infection with hepatitis C virus (HCV) may suppress co-infection with hepatitis B virus (HBV) during acute or chronic HBV infection. We examined relationships between HBV infection, HCV infection and other factors among injection drug users (IDUs) with antibodies to both viruses. Participants enrolled in a cross-sectional study during 1998-2000 were considered to have been infected with HBV if they had core antibody, to be chronically infected if they had hepatitis B surface antigen (HBsAg), to have been infected with HCV if they had HCV antibody and to be chronically infected if they had HCV RNA. Among 1694 participants with antibody to both viruses, HBsAg prevalence decreased with increasing age among those positive for HCV RNA [from 4.55% in those 18-29 years to 1.03% in those >or=50 years old (P(trend) = 0.02)], but not among those who were negative for HCV RNA. Chronic HBV infection was less common overall among those with chronic HCV infection (odds ratio [OR], 0.25; P < 0.0001), but this inverse relationship was much stronger in the oldest (>50 years; OR = 0.15) than the youngest (18-29 years; OR = 0.81) participants (P(trend) = 0.03). Similar results were obtained when duration of injection drug use was substituted for age (P(trend) = 0.05). Among IDUs who have acquired both HBV and HCV, chronic HBV infection is much less common among those with chronic HCV infection, but this inverse relationship increases markedly with increasing years of age and injection drug use. Co-infection with HCV may enhance the resolution of HBsAg during the chronic phases of these infections.

Studies of the genomic RNA of leukosis viruses: implications for RNA dimerization.

Retroviral particles contain two positive-strand genomic RNAs linked together by noncovalent bonds that can be dissociated under mild conditions. We studied genomic RNAs of wild-type and mutant avian leukosis viruses (ALVs) in an attempt to (i) better understand the site(s) of RNA dimerization, (ii) examine whether the primer binding site (PBS) and tRNA primer are involved in dimerization, and (iii) determine the structure of genomic RNA in protease-deficient (PR(-)) mutants. We showed that extensively nicked wild-type ALV genomic RNAs melt cooperatively. This implies a complex secondary and/or tertiary structure for these RNAs that extends well beyond the 5' dimerization site. To investigate the role of the PBS-tRNA complex in dimerization, we analyzed genomic RNAs from mutant viruses in which the tRNA(Trp) PBS had been replaced with sequences homologous to the 3' end of six other chicken tRNAs. We found the genomic RNAs of these viruses are dimers that dissociate at the same temperature as wild-type viral RNA, which suggests that the identity of the PBS and the tRNA primer do not affect dimer stability. We studied two ALV PR(-) mutants: one containing a large (>1.9-kb) inversion spanning the 3' end of gag and much of pol, rendering it deficient in PR, reverse transcriptase, and integrase, and another with a point mutation in PR. In both of these mutant viruses, the genomic RNA appears to be either primarily or exclusively monomeric. These data suggest that ALV can package its RNA as monomers that subsequently dimerize.

Placement of tRNA primer on the primer-binding site requires pol gene expression in avian but not murine retroviruses.

In an early step in the retroviral infectious process, reverse transcriptase copies the genomic RNA of the virus into complementary minus-strand DNA. The primer for this synthetic event is a molecule of cellular tRNA, which is annealed by its 3' 18 nucleotides to a region of the genomic RNA termed the primer-binding site (PBS); the sequence of the PBS and hence the identity of the tRNA depend upon the retrovirus species. In addition to the primer tRNA, retrovirus particles contain a substantial number of other tRNA molecules. The latter tRNA population is enriched for the tRNA species which serves as primer for the virus. While there is considerable evidence that the enrichment for the primer species can be attributed to the pol gene product, nothing is known regarding mechanisms of annealing the primer to the PBS. We have analyzed pol- mutants of avian leukosis virus (ALV) and murine leukemia virus (MuLV) for the presence of primer at the PBS in virion genomic RNA. Remarkably, the results were different for the two viruses: the PBS was substantially occupied by primer in MuLV but not in ALV. Previous data indicates that the Pol-dependent enrichment of the primer within the virion is much greater in ALV than in MuLV. We therefore propose that the absence of primer at the PBS in pol- ALV is due to the deficiency of the primer species within the particle. The results suggest that, at least in MuLV, the tRNA is unwound by either the Gag protein or a cellular protein for annealing to the PBS. Further, the C-terminal 17 amino acids of Gag are unnecessary for this function in MuLV.

Replication of avian leukosis viruses with mutations at the primer binding site: use of alternative tRNAs as primers.

We have tested whether avian leukosis viruses (ALVs) can use tRNAs other than tRNATrp to initiate reverse transcription. The primer binding site (PBS) of a wild-type ALV provirus, which is complementary to the 3' end of tRNA(Trp), was replaced with sequences homologous to the 3' ends of six different chicken tRNAs (tRN(APro), tRNA(Lys), tRNA(Met), tRNA(Ile), tRNA(Phe), and tRNA(Ser)). Transfection of these proviruses into chicken embryo fibroblasts resulted in the production of infectious viruses, all of which apparently used the tRNA specified by the mutated PBS to replicate. However, growth of these viruses resulted in reversion to the wild-type (tRNA(Trp)) PBS. Some of the viruses revert quite quickly, while others are more stable. The relative stability of a given PBS correlated with the concentration of the corresponding tRNA in the virion. We determined the percentage of viral RNA that had a tRNA bound to the PBS and found that the occupancy rate is lower in the mutants than in the wild-type virus. We conclude that many different tRNAs can be used as primers to initiate reverse transcription in ALV. However, ALVs that use tRNA(Trp) have a growth advantage over ALVs that use other tRNAs.

Ribosomal RNA phylogenies for the vibrio-enteric group of eubacteria.

Comparisons between the ribonucleotide sequences of 5S rRNAs of the Gram-negative eubacteria indicate that several families, namely Enterobacteriaceae, Vibrionaceae and Aeromonadaceae possess remarkably similar evolutionary histories. A study of the phylogenetic relationships among these groups, through cluster analysis and construction of evolutionary trees, suggests the existence of dissimilar rates of evolution along the several lineages. These dissimilarities are most evident in comparisons between the phylogenetic depths of the Enterobacteriaceae and Vibrionaceae. Detection of disparate rates of evolution, as well as their influence on the interpretation of the natural taxonomy of this group of bacteria, is discussed.