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Significance of premature stop codons in env of simian immunodeficiency virus
T Kodama1, D P Wooley, Y M Naidu
1New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772.
Abstract:
The location of the translational termination codon for the transmembrane protein (TMP) varies in three infectious molecular clones of simian immunodeficiency virus from macaques (SIVmac). The SIVmac251 and SIVmac142 infectious clones have premature stop signals that differ in location by one codon; transfection of these DNAs into human HUT-78 cells yielded virus with a truncated TMP (28 to 30 kilodaltons [kDa]). The SIVmac239 infectious clone does not have a premature stop codon in its TMP-coding region. Transfection of HUT-78 cells with this clone initially yielded virus with a full-length TMP (41 kDa). At 20 to 30 days posttransfection, SIVmac239 virus with a 41-kDa TMP gradually disappeared coincident with the emergence of a virus with a 28-kDa TMP. Virus production dramatically increased in parallel with the emergence of a virus with a 28-kDa TMP. Sequence analysis of viral DNAs from these cultures showed that premature stop codons arising by point mutation were responsible for the change in size of the TMP with time. A similar selective pressure for truncated forms of TMP was observed when the SIVmac239 clone was transfected into human peripheral blood lymphocytes (PBL). In contrast, no such selective pressure was observed in macaque PBL. When the SIVmac239 clone was transfected into macaque PBL and the resultant virus was serially passaged in macaque PBL, the virus replicated very well and maintained a 41-kDa TMP for 80 days in culture. Macaque monkeys were infected with SIVmac239 having a 28-kDa TMP; virus subsequently recovered from T4-enriched lymphocytes of peripheral blood showed only the 41-kDa form of TMP. These results indicate that the natural form of TMP in SIVmac is the full-length 41-kDa TMP, just as in human immunodeficiency virus type 1. Viruses with truncated forms of TMP appear to result from mutation and selection during propagation in unnatural human cells.
Insights
Truncated transmembrane protein (TMP) forms in simian immunodeficiency virus (SIVmac) arise from mutations during propagation in human cells, not in natural macaque hosts. The full-length TMP is the natural form in SIVmac.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Simian immunodeficiency virus (SIVmac) is a lentivirus that infects macaques and is related to human immunodeficiency virus (HIV).
- The transmembrane protein (TMP) is a critical component of the viral envelope, mediating entry into host cells.
Purpose of the Study:
- To investigate the variation in TMP length among different SIVmac infectious clones.
- To determine the factors influencing TMP truncation during viral propagation in different cell types.
Main Methods:
- Transfection of SIVmac infectious clones into human and macaque cell lines (HUT-78 cells and peripheral blood lymphocytes - PBL).
- Analysis of TMP size by Western blot and sequencing of viral DNA to identify mutations.
- Infection of macaque monkeys with SIVmac and analysis of recovered virus.
Main Results:
- SIVmac251 and SIVmac142 clones produced truncated TMP (28-30 kDa) in human cells.
- SIVmac239 initially produced full-length TMP (41 kDa) in human cells, but truncated TMP emerged over time due to point mutations.
- Truncated TMP was favored in human cells, while full-length TMP was maintained in macaque PBL and in vivo.
Conclusions:
- The natural form of SIVmac TMP is full-length (41 kDa), similar to HIV-1.
- Truncated TMP variants arise from mutation and selection pressure during propagation in non-natural human cell environments.
- These findings highlight the importance of host cell context in viral evolution and protein expression.