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Journal of Virology, August 2003, p. 8584-8587, Vol. 77, No. 15
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.15.8584-8587.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Structural and Evolutionary Analysis of an Orangutan Foamy Virus
Ernst J. Verschoor,1* Susan Langenhuijzen,1 Saskia van den Engel,1 Henk Niphuis,1 Kristin S. Warren,2 and Jonathan L. Heeney1
Department of Virology, Biomedical Primate Research Centre, Rijswijk, The Netherlands,1
Division of Veterinary and Biomedical Sciences, Murdoch University, Western Australia, Australia2
Received 3 March 2003/
Accepted 30 April 2003

ABSTRACT
The full-length proviral genome of a foamy virus infecting a
Bornean orangutan was amplified, and its sequence was analyzed.
Although the genome showed a clear resemblance to other published
foamy virus genomes from apes and monkeys, phylogenetic analysis
revealed that simian foamy virus SFVora was evolutionarily equidistant
from foamy viruses from other hominoids and from those from
Old World monkeys. This finding suggests an independent evolution
within its host over a long period of time.

TEXT
Foamy viruses (FVs) are a subfamily of retroviruses that cause
persistent but benign infections in their natural hosts. Because
of the harmless nature of FV infections and their extremely
broad cell tropism, they are of great interest in the development
of FV-derived vectors for vaccines and gene therapy. In primates,
FVs have been isolated from monkeys and great apes (
3,
4,
6,
31). Furthermore, infections of humans with FVs have been described
(
1,
5,
14,
28,
30). Only a few full-length simian foamy virus
(SFV) genomes have been determined, including those for SFV-1
and SFV-2, viruses obtained from Japanese macaques (renamed
SFVmac); SFV-3 (SFVagm), derived from an African green monkey;
and SFVcpz and SFVcpz(hu), isolated from chimpanzees and humans,
respectively (
12,
15,
17,
19,
22,
26). The genomes of other
great ape FVs, from gorillas, pygmy chimpanzees, and orangutans,
have been partially characterized. An orangutan virus, designated
SFVora (formerly named SFV-11), has been isolated, and a partial
long-terminal-repeat (LTR) nucleotide sequence has been determined
(
20). To broaden our knowledge of the diversity and variability
of SFVs, in particular those infecting great apes, we have sequenced
the genome of an SFV isolated from a Bornean orangutan (
Pongo pygmaeus pygmaeus).
Blood samples were obtained from orangutans that were housed at the Wanariset Orangutan Reintroduction Center in East Kalimantan, Indonesia. The samples were assayed for antibodies to FV antigens to determine the incidence of infection (34). Of the 108 animals tested, 69.4% were seropositive by the assay. From one seropositive animal, Bella, genomic DNA was isolated and used as a template for the amplification of overlapping PCR fragments representing the complete genome of the virus.
The genome was amplified in three segments. First, a 425-bp pol fragment was amplified in a nested PCR (33). The two reverse PCR primers from that reaction were then used in combination with two forward LTR primers that had been used previously to amplify a small sequence of SFVora. Amplification resulted in a 4,777-bp 5' LTR-to-pol fragment. Two primers, env/for (5'-TTATATTGGACCCTTGCCTCCTTCCAACGGTTATTTACAT-3') and env/rev (5'-GGATTATTGTATATTGATTATCCTTAGGGAAGTTCGCCAG-3'), were then designed to bind to the pol (env/for primer) and LTR-to-pol (env/rev primer) fragments. Use of these primers in a single reaction yielded a 6,623-bp fragment that extended from pol into the 3' LTR. Both long PCRs were performed by using the eLONGase amplification system (Life Technologies B.V., Breda, The Netherlands) with an MgCl2 concentration of 1.9 mM. The amplification was performed for 35 cycles, each consisting of 30 s of denaturation at 94°C, 30 s of annealing at 65°C, and a 9-min elongation step at 68°C. The PCR products were isolated from agarose gel by using a QIAquick gel extraction kit (Qiagen, Hilden, Germany) and were cloned in the pGEM-T Easy vector (Promega Corporation, Madison, Wis.). They were sequenced by using the ABI PRISM BigDye Terminator version 3.0 cycle sequencing kit on an ABI PRISM 310 Genetic Analyzer (Applied Biosystems). Sequence analysis was performed with MacVector 6.0 and AssemblyLIGN (Oxford Molecular Ltd.) software packages.
The borders of the LTRs were determined by alignment and comparison with SFVcpz. The proviral genome of the virus, SFVora, was calculated to be 12,823 bp long. The organization of open reading frames (ORF) in SFVora is typical for FVs, with three genes (gag, pol, and env) encoding the structural proteins, in addition to the small Tas and Bel-2 ORFs.
The LTRs were estimated to be 1,621 bp long. The lengths of the U3, R, and U5 regions of the LTR are 1,286, 177, and 158 bp, respectively (Fig. 1). Comparison of a 322-nucleotide (nt) LTR fragment revealed 95% identity between SFVora derived from Bella and the SFV-11 sequence from the orangutan Dodo (20). Analogous to SFVcpz, SFVora has a transcription initiation signal (TATAA box) at position 1258, just upstream from the U3-R junction within the conserved cap site (GGGA) (37) (15), and its polyadenylation site (AATAAA) is located at nt 1438. In the U3 region, two Ets-1 and one AP-1 transcription factor recognition sites are situated at nt 328, 335, and 614, respectively.
Outside the LTR, two sites involved in the RNA dimerization
process, SI and SII, are recognized (
7,
10), with the latter
overlapping the primer binding site (nt 1625 to 1642). The polypurine
tract (AGAGAGGAGAGGG) is located at nt 11188 to 11201.
The gag gene starts at position 1716 and encodes a protein of 624 amino acids (aa). Gag contains three glycine-arginine-rich stretches (GR-I, GR-II, and GR-III; aa 462 to 492, 518 to 541, and 563 to 596, respectively) which are involved in the binding of nucleic acid and in the nuclear localization of the Gag precursor (29). A conserved arginine residue that acts in the intracellular capsid assembly is located at aa position 46 (9). A stretch of regularly spaced hydrophobic residues that may form a coiled-coil motif necessary for Gag-Gag interaction during viral capsid formation extends from aa 125 to 187 (36). Several putative proteolytic cleavage sites, located at positions 285 to 292 (QHIR
AVTG), 313 to 320 (EGVY
PVTT), 326 to 333 (RIIN
ALIG), and 596 to 603 (HAVN
AVTQ), can be identified (23). However, only the last site appears to be efficiently recognized by the viral protease and may be essential for viral infectivity (18). The ORF of the Pol precursor extends from nt 3547 to 6984 and encodes 1,145 aa. The catalytic domains of the reverse transcriptase (RT) moiety (Y312VDD315) are identical in all FVs (27). The putative proteolytic cleavage sites within Pol are predicted at H140WEN
QVGH147 (protease-RT cleavage site) and S593MVF
YTGD600 (RT-RNase H cleavage site; identical to that of SFVagm), while the RNase H-integrase cleavage site (Y748VVN
NIIK755) is unique among SFVs (24). The env ORF (nt 6923 to 9892) encodes 989 aa. A signal peptide of 18 aa residues (RTLAWLFLFCVLLIVVLV) is predicted at positions 67 to 84, generating a leader protein of 86 aa (38). The cleavage site between the surface (SU) and transmembrane (TM) glycoproteins (R572NRR575
) (2, 8) generates SU and TM glycoproteins of 486 and 417 aa, respectively. Located in the N terminus of the TM protein is a fusion peptide containing conserved hydrophobic residues (L581-XX-M584-XXX-L588-XX-A591-V592-XX-L595-XX-I598). The charged residues in the membrane-spanning domain of TM (25), in addition to the endoplasmic reticulum retrieval signal (K988RK990), are all conserved in the TM protein (2, 13, 38). On the basis of a comparison with SFVcpz(hu), an internal promoter sequence was identified at nt 9583 to 9638 within the env gene [88 and 91% similarity with the SFVcpz(hu) and SFVcpz promoters, respectively]. Two smaller ORFs that encode the accessory proteins Tas and Bet can be distinguished. The Tas ORF is located at positions 9862 to 10698 and encodes a protein of 278 aa. The Bel-2 ORF has a coding capacity of 321 aa (positions 10589 to 11554).
The SFVora Gag protein has relatively low identity with other primate SFV Gag proteins compared to that of the polymerase and envelope proteins (Table 1). This is in agreement with the findings of others (32, 38). In this respect, FVs resemble the primate T-lymphotropic viruses more than the immunodeficiency viruses (16, 21). Unlike human immunodeficiency virus, FVs and the primate T-lymphotropic viruses are highly cell associated in vivo, with cell-free virus rarely being detectable in the blood, suggesting either cell-to-cell spread or dissemination by clonal expansion. Such evolutionarily acquired viral strategies may preclude the necessity of the virus to accumulate envelope mutations to escape the surveillance of the immune system (11, 32, 39).
Surprisingly, the protein sequence identities of SFVora with
SFVcpz(hu) and SFVcpz were only slightly higher than those with
the viruses from Old World monkeys, which suggests an equidistant
evolutionary relationship of SFVora with FVs from monkeys and
other great apes. Phylogenetic analysis of the different proteins
confirmed this notion (data not shown). To validate our assumption,
we expanded our data set by using 425-bp fragments of the
pol gene from GenBank and EMBL databases to establish the evolutionary
relationships between a larger set of primate FVs. In addition,
the
pol region from another SFVora (isolate Jabba; 98% identity
with SFVora isolate Bella) was added to the data set. Phylogenetic
analysis of
pol sequences was performed by using PAUP 4.0 B10
beta (
35), and the phylogenetic tree is depicted in Fig.
2.
The tree was rooted with the only FV sequence available from
a New World monkey (SFV-8 from a spider monkey). Viruses isolated
from Old World monkeys from Africa (SFVbab, SFVagm, SFVsmm)
and Asia (SFVmac) and those from humans and common and pygmy
chimpanzees form two monophyletic groups, both identified with
100% confidence. From our data it is evident that SFVora is
distinct from other known SFVs. SFVora does not cluster with
either the African great ape viruses or other SFVs. The evolutionary
distances between the most closely related members of each group
and SFVora were 0.3657 (SFVbab10) and 0.3810 (SFVpyg). Our analyses
indicate that FVs from orangutans share a common ancestor virus
with other primate FVs but that SFVora has evolved independently
in its host over a long time period.
Nucleotide sequence accession number.
The sequence of SFVora strain Bella has been deposited in the
EMBL sequence database under accession number
AJ 544579.

ACKNOWLEDGMENTS
We thank Dr. Heriyanto and the staff at the Wanariset Orangutan
Reintroduction Centre for assistance with sample collection,
M. O. McClure, O. Erlwein, and M. Schweizer for serological
analyses and helpful discussions, and N. Otting, N. de Groot,
and colleagues at the Biomedical Primate Research Centre for
support and technical assistance.
This work was supported by the EC grant BMH4-CT97-2010.

FOOTNOTES
* Corresponding author. Mailing address: Biomedical Primate Research Centre (BPRC), Department of Virology, P.O. Box 3306, 2280 GH Rijswijk, The Netherlands. Phone: 31-15-284-2592. Fax: 31-15-284-3986. E-mail:
verschoor{at}bprc.nl.


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Journal of Virology, August 2003, p. 8584-8587, Vol. 77, No. 15
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.15.8584-8587.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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