Mapping the determinants of EIAV restriction by Fv1 from <i>M. m. spretus</i>.

<p>(A) Analysis of restriction by chimeric Fv1 constructs. (B) Analysis of restriction by site directed mutant forms of Fv1.</p

Sources of Fv1 clones.

a<p>LGP, a gift from Drs Francois Bonhomme and Jean-Louis Guénet, Laboratoire Genome et Populations, Montpellier, France; JMC, a gift from Dr John Coffin, Tufts University, Boston, USA; BAM, a gift from Dr Beverley Mock, NCI, Bethesda, USA; TJL, purchased from the Jackson Laboratory, Bar Harbor, USA; MDTF, <i>M.dunni</i> tail fibroblast cells <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat.1003968-Lander1" target="_blank">[65]</a>.</p

Events in the evolution of the <i>Fv1</i> gene.

<p>A phylogenetic tree showing the approximate times of <i>Fv1</i> acquisition and hypothetical virus infections leading to selection of new retroviral restriction activities. Colored mice indicate <i>Fv1</i> activity against at least one virus.</p

Features of Fv1.

<p>At the top of the figure is a schematic of the Fv1 protein showing the relative positions of the previously mapped functional domains including coiled coil and major homology regions as well as the host range specificity regions previously defined by a comparison of Fv1ⁿ and Fv1^b<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat.1003968-Bishop2" target="_blank">[48]</a>. Below is shown the positions of four variable regions (V_A–D), the amino acid differences that define them and the number of times each amino acid occurs. Based on a comparison of 19 mice (<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat-1003968-t001" target="_blank">Table 1</a> plus <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat-1003968-t002" target="_blank">Table 2</a>).</p

Restriction activity of various Fv1s against different MLVs.

<p>Restriction activity of various Fv1s against different MLVs.</p

Properties of the variable regions of Fv1.

<p>Proteins corresponding to the Fv1SPR1, Fv1CAR1 and Fv1^nr alleles are illustrated. Shaded positions indicate amino acids showing positive selection <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat.1003968-Yan1" target="_blank">[40]</a>, residues in triangles have been implicated in restriction specificity (this paper, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat.1003968-Stevens1" target="_blank">[16]</a>, <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003968#ppat.1003968-Bishop2" target="_blank">[48]</a>).</p

Evolution of the Retroviral Restriction Gene <i>Fv1</i>: Inhibition of Non-MLV Retroviruses

<div><p>Fv1 is the prototypic restriction factor that protects against infection by the murine leukemia virus (MLV). It was first identified in cells that were derived from laboratory mice and was found to be homologous to the <i>gag</i> gene of an endogenous retrovirus (ERV). To understand the evolution of the host restriction gene from its retroviral origins, <i>Fv1</i>s from wild mice were isolated and characterized. Most of these possess intact open reading frames but not all restricted N-, B-, NR-or NB-tropic MLVs, suggesting that other viruses could have played a role in the selection of the gene. The Fv1s from <i>Mus spretus</i> and <i>Mus caroli</i> were found to restrict equine infectious anemia virus (EIAV) and feline foamy virus (FFV) respectively, indicating that Fv1 could have a broader target range than previously thought, including activity against lentiviruses and spumaviruses. Analyses of the <i>Fv1</i> sequences revealed a number of residues in the C-terminal region that had evolved under positive selection. Four of these selected residues were found to be involved in the novel restriction by mapping studies. These results strengthen the similarities between the two capsid binding restriction factors, <i>Fv1</i> and TRIM5α, which support the hypothesis that <i>Fv1</i> defended mice against waves of retroviral infection possibly including non-MLVs as well as MLVs.</p></div

Staging restriction blocks in novel <i>Fv1</i>s.

<p>MDTF cells were transduced with <i>Fv1CAR1</i> and <i>Fv1SPR1</i>, then stable Fv1-expressing cell lines selected and tested for restriction of virus replication by FACS (A, B) or by PCR to measure viral DNA synthesis or formation of circular viral DNA containing two LTRs (C, D).</p

Mapping the determinants of FFV restriction by Fv1 from <i>M. m. caroli</i>.

<p>(A) Analysis of restriction by chimeric Fv1 constructs. (B) Analysis of restriction by site directed mutant forms of Fv1.</p

Restriction activity of various Fv1s against different viruses.

<p>Restriction activity of various Fv1s against different viruses.</p