HIV-1 integrase anchors viral RNA inside the capsid: a structural study with no direct FeLV data
Nature · 2026
In plain language
This study is about HIV-1, a human virus, not FeLV or cats. In the laboratory, the authors looked at how an HIV-1 protein called integrase helps keep the virus's genetic material inside its inner shell, the capsid. The paper gives no direct evidence about FeLV. Any link to FeLV is indirect and unproven.
Scientific detail
This is a retrovirus biology and mechanism paper, published in Nature in 2026, based on in vitro experiments with HIV-1 and with SIVtal and other primate lentiviral integrase systems. The authors determined a cryo-EM structure of primate lentiviral integrase in complex with RNA, which formed a linear filament of integrase octamer repeat units. In the SIVtal integrase-RNA TAR structure, integrase tetramers engage RNA chains solely through their C-terminal domains.
The repeat spacing of the HIV-1 integrase filament matches the 91 Å spacing of the mature HIV-1 capsid hexamer lattice. In addition, substitutions in residues involved in integrase-capsid contacts produced eccentric virions with RNA nucleoids outside the cores. Together, the data support a role for HIV-1 integrase in promoting encapsidation of viral genomic RNA into mature viral cores.
For virus-based experiments, results are presented as mean ± s.d. of at least n = 3 independent experiments; cryo-EM/cryo-ET particle and subtomogram counts are given in the methods (for example, 58,103 and 46,116 particles for final reconstructions and 594 subtomograms for one subtomogram averaging reconstruction). The authors state that investigators were not blinded to sample identity and outcome assessment owing to practical constraints.
Relevance to FeLV is indirect only. The study does not examine feline leukemia virus, cats, FeLV proteins, FeLV infection or FeLV treatment. The findings do not establish that FeLV integrase has the same function, domain arrangement or capsid geometry; any application to FeLV would require FeLV-specific experimental validation.
What we know
In HIV-1 and in SIVtal and primate lentiviral integrase systems, there is structural and in vitro experimental evidence that integrase binds RNA, forms filaments whose spacing matches the mature capsid lattice, and contributes to positioning RNA inside the viral core. These results come from cell culture systems, purified viral cores and computational simulations.
What we don't know
It is not known whether FeLV integrase does anything equivalent: this paper offers no evidence in cats or in FeLV. It is also unknown whether the domain arrangement or capsid geometry is analogous in FeLV. That would require FeLV-specific studies.
Evidence
EvidenceLevel D — Indirect evidence: other species or retrovirusConfidence 98/100
HIV-1 integrase promotes encapsulation of viral genomic RNA into mature viral cores.
Excerpt verified in the source — verbatim, in the source's own language“HIV-1 integrase (IN) promotes encapsulation of viral genomic RNA into mature viral cores, and this function is a target for ongoing antiretroviral drug development efforts 1-3 .”
This directly supports a role for HIV-1 integrase in genomic RNA encapsulation into mature HIV-1 cores. It does not establish the same function for FeLV integrase or any feline system.
EvidenceLevel D — Indirect evidence: other species or retrovirusConfidence 98/100
The authors determined a cryo-EM structure of primate lentiviral integrase in complex with RNA that formed a linear filament of integrase octamer repeat units.
Excerpt verified in the source — verbatim, in the source's own language“Here we determined the cryogenic electron microscopy (cryo-EM) structure of a primate lentiviral IN in a complex with RNA, revealing a linear filament made of IN octamer repeat units, each comprising a pair of asymmetric homotetramers.”
This is direct structural evidence for a primate lentiviral integrase-RNA filament architecture. It is not direct evidence about FeLV, cats, clinical disease, or treatment.
EvidenceLevel D — Indirect evidence: other species or retrovirusConfidence 97/100
In the SIVtal integrase-RNA TAR cryo-EM structure, integrase tetramers engage RNA chains solely through their C-terminal domains.
Excerpt verified in the source — verbatim, in the source's own language“The tetramers engage RNA chains solely through their CTDs.”
This identifies the C-terminal domains as the RNA-engaging domains in the reported SIVtal integrase-RNA structure. It does not prove that FeLV integrase uses the same domain arrangement.
EvidenceLevel D — Indirect evidence: other species or retrovirusConfidence 96/100
HIV-1 integrase filament repeat spacing matches the mature HIV-1 capsid hexamer lattice spacing of 91 Å.
Excerpt verified in the source — verbatim, in the source's own language“The spacing between unit cells in the mature CA lattice (hexamers) and in the IN filament (octamers) is identical - 91 Å, as indicated by arrows.”
This supports geometric compatibility between HIV-1 integrase filaments and the mature HIV-1 capsid lattice. It does not establish analogous capsid-integrase geometry for FeLV.
EvidenceLevel D — Indirect evidence: other species or retrovirusConfidence 98/100
Substitutions in residues involved in HIV-1 integrase-capsid contacts produced eccentric virions with RNA nucleoids outside the cores.
Excerpt verified in the source — verbatim, in the source's own language“Substitutions of residues involved in IN-CA contacts yielded eccentric virions with RNA nucleoids located outside of the cores.”
This supports the importance of HIV-1 integrase-capsid contacts for RNA nucleoid placement within cores. It does not establish a FeLV intervention, treatment, or clinical recommendation.
Open questionConfidence 95/100
The paper does not provide direct evidence about FeLV or cats.
The source concerns HIV-1, SIVtal/primate lentiviral integrase, cell culture systems, purified viral cores, and computational simulations. Any application to FeLV remains indirect and requires FeLV-specific experimental validation.
Provenance
Source: Integrase anchors viral RNA to the HIV-1 capsid interior.
AVA