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PubMed2002

Sustained high proportion of zidovudine-resistant HIV variants despite prolonged substitution of zidovudine by other nucleoside reverse transcriptase inhibitors.

The consequences of zidovudine (ZDV) replacement by other nucleoside reverse transcriptase inhibitors on the expression of resistance mutations at codons 215 and 41 of the reverse transcriptase (RT) gene was investigated prospectively in 66 patients harboring mutant genotypes who were changed to an effective two- or three-drug combination antiretroviral regimen. Quantitation of mutant (MUT) viral populations at codon 215 by means of RT-PCR with differential hybridization of amplicons specific for MUT and wild (WT) variants revealed no difference in the proportion of 215 MUT variants prior to (93.5 +/- 2.4%) and 12 to 20 months after (96.9 +/- 1.9%) ZDV replacement, independently of a therapeutic change for stavudine. The fitness of the variants harboring the ZDV-resistant MUT 215 genotype following drug withdrawal was calculated to be 96 to 99% of that of the variants harboring the WT 215 genotype. The apparent stability of ZDV-resistant variants in the study population may have two main complementary explanations: persistent selective pressure secondary to partial cross-resistance due to the new regimens given after the therapeutic alteration and suppression of viral replication after the therapeutic alteration that could have hampered the replacement of less fit variants by fitter variants. These findings indicate that, at least within 15 months following discontinuation of ZDV, an effective antiretroviral therapy is insufficient to allow for ZDV-resistant strains to disappear, and thus to allow for the safe re-introduction of the drug.

Adaptation, Physiological↗

PubMed2026

Selectivity Filter KCND3 Variant Causes Spinocerebellar Ataxia 19/22 and KV4.3 Functional Loss.

BACKGROUND: Spinocerebellar ataxia type 19/22 (SCA19/22) is a rare autosomal dominant neurodegenerative disorder caused by KCND3 variants encoding the KV4.3 potassium channel. While most pathogenic variants result in loss-of-function (LOF), no pathogenic variants were previously identified in the channel's selectivity filter, a critical domain for ion selectivity. OBJECTIVES: To elucidate the genetic cause and functional LOF mechanisms underlying severe early-onset cerebellar ataxia and neurodevelopmental impairment in monozygotic twins. METHODS: We evaluated twins presenting with early-onset cerebellar ataxia, developmental delay, and cognitive impairment. Whole-exome sequencing (WES) identified a KCND3 c.1103T>C (p.L368P) variant. Functional impacts were assessed through HEK293T cell protein expression, Xenopus oocyte electrophysiology, and structural homology modeling. RESULTS: WES identified a heterozygous de novo p.L368P variant in the "TLGYG" selectivity filter sequence. Modeling predicted a pore radius reduction, blocking potassium permeation. Biochemical analyses revealed markedly reduced protein expression and impaired trafficking. Electrophysiological recordings confirmed complete potassium current loss and a strong dominant-negative effect on wild-type KV4.3 currents. Clinically, the twins exhibited severe intellectual disability, developmental delay, and cerebellar atrophy with pontine flattening, without epilepsy. CONCLUSIONS: Identifying the first pathogenic variant in the KV4.3 selectivity filter highlights its critical role in channel proteostasis and ion conductance. The p.L368P variant produces a pronounced LOF phenotype and broadens the SCA19/22 clinical spectrum, indicating the filter's structural integrity is a key determinant of disease severity. © 2026 International Parkinson and Movement Disorder Society.

KCND3↗

PubMed2026

Molecular Characterisation of Treacher Collins Syndrome in a South African Cohort: Novel Disease-Causing Variants in TCOF1 and POLR1D.

BACKGROUND: Treacher Collins syndrome (TCS) is a rare craniofacial disorder characterised by variable expressivity. It is caused by pathogenic variants in the TCOF1, POLR1D, POLR1C, or POLR1B genes. Common clinical features include hypoplasia of the zygomatic complex and mandible, downward-slanting palpebral fissures, lower eyelid anomalies, microtia, and hearing loss. Owing to its phenotypic overlap with other craniofacial syndromes, molecular testing is essential for establishing an accurate diagnosis and guiding effective clinical management. METHODS: Ten South African patients with a suspected clinical diagnosis of TCS underwent targeted next-generation sequencing (NGS) using a custom gene panel including TCOF1, POLR1C, and POLR1D genes. Variants were classified according to ACMG/AMP guidelines, with validation by Sanger sequencing where necessary. RESULTS: Disease-causing variants were identified in six of the ten patients (60%). These included five heterozygous variants in TCOF1 and one homozygous variant in POLR1D. Notably, five of the six variants were identified for the first time in this study. Additionally, a recurrent TCOF1 deletion was identified for the first time in an African family. CONCLUSION: This study expands the mutational spectrum of TCS in general and provides African data in particular. Findings support the use of panel-based NGS for diagnosis in resource-limited settings and highlight the need for population-specific variant data to improve diagnostic accuracy, guide clinical care, and support genetic counselling for affected individuals and their families.

Humans↗

PubMed1997

Thermal denaturation of iso-1-cytochrome c variants: comparison with solvent denaturation.

Thermal denaturation studies as a function of pH were carried out on wild-type iso-1-cytochrome c and three variants of this protein at the solvent-exposed position 73 of the sequence. By examining the enthalpy and Tm at various pH values, the heat capacity increment (delta Cp), which is dominated by the degree of change in nonpolar hydration upon protein unfolding, was found for the wild type where lysine 73 is normally present and for three variants. For the Trp 73 variant, the delta Cp value (1.15 +/- 0.17 kcal/mol K) decreased slightly relative to wild-type iso-1-cytochrome c (1.40 +/- 0.06 kcal/mol K), while for the Ile 73 (1.65 +/- 0.07 kcal/mol K) and the Val 73 (1.50 +/- 0.06 kcal/mol K) variants, delta Cp increased slightly. In previous studies, the Trp 73, Ile 73, and Val 73 variants have been shown to have decreased m-values in guanidine hydrochloride denaturations relative to the wild-type protein (Hermann L, Bowler BE, Dong A, Caughey WS. 1995. The effects of hydrophilic to hydrophobic surface mutations on the denatured state of iso-1-cytochrome c: Investigation of aliphatic residues. Biochemistry 34:3040-3047). Both the m-value and delta Cp are related to the change in solvent exposure upon unfolding and other investigators have shown a correlation exists between these two parameters. However, for this subset of variants of iso-1-cytochrome c, a lack of correlation exists which implies that there may be basic differences between the guanidine hydrochloride and thermal denaturations of this protein. Spectroscopic data are consistent with different denatured states for thermal and guanidine hydrochloride unfolding. The different response of m-values and delta Cp for these variants will be discussed in this context.

Circular Dichroism↗

PubMed1998

Structure and stability of the P93G variant of ribonuclease A.

The peptide bonds preceding Pro 93 and Pro 114 of bovine pancreatic ribonuclease A (RNase A) are in the cis conformation. The trans-to-cis isomerization of these bonds had been indicted as the slow step during protein folding. Here, site-directed mutagenesis was used to replace Pro 93 or Pro 114 with a glycine residue, and the crystalline structure of the P93G variant was determined by X-ray diffraction analysis to a resolution of 1.7 A. This structure is essentially identical to that of the wild-type protein, except for the 91-94 beta-turn containing the substitution. In the wild-type protein, the beta-turn is of type VIa. In the P93G variant, this turn is of type II with the peptide bond preceding Gly 93 being trans. The thermal stabilities of the P93G and P114G variants were assessed by differential scanning calorimetry and thermal denaturation experiments monitored by ultraviolet spectroscopy. The value of delta deltaGm which reports on the stability lost in the variants, is 1.5-fold greater for the P114G variant than for the P93G variant. The greater stability of the P93G variant is likely due to the relatively facile accommodation of residues 91-94 in a type II turn, which has a preference for a glycine residue in its i + 2 position.

Amino Acid Substitution↗

PubMed2004

Identification and characterization of a new beta-casein variant in goat milk by high-performance liquid chromatography with electrospray ionization mass spectrometry and matrix-assisted laser desorption/ionization mass spectrometry.

A new variant of beta-casein was detected in the casein fraction obtained from milk of a goat belonging to an autochthonous breed of southern Italy, "Argentata dell'Etna". Reversed-phase high-performance liquid chromatography/electrospray ionization mass spectrometry (RP-HPLC/ESI-MS) analysis indicated that the new beta-casein variant, here named D, has a M(r) 15 Da higher than that of variant C previously described. The modification in the amino acid sequence responsible for the 15 Da difference in M(r) between variants C and D was determined by coupling trypsin digestion with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and RP-HPLC/ESI-MS, and it was demonstrated that it is due to the point mutation Val(207) --> Asn(207). The phosphorylation pattern of the new variant D was shown to be identical to that of variant C, as the protein shows two phosphorylation levels, 5 and 6P, occurring with comparable relative abundances. Ser35 was determined as one of the phosphorylation sites, whereas the others were probably analogous to those determined previously for the beta-Cn variant C, at Thr12 and Ser1517-19. The results reported here indicate that the combined use of RP-HPLC/ESI-MS, MALDI-TOFMS and MS/MS represents a powerful tool for the detection and characterization of minor components present in complex protein mixtures.

Amino Acid Sequence↗

PubMed2000

Differential effect toward inhibition of papain and cathepsin C by recombinant human salivary cystatin SN and its variants produced by a baculovirus system.

Human salivary cystatin SN (CsnSN) is a member of the cystatin superfamily of cysteine proteinase inhibitors. In this study we used a baculovirus expression system to produce a full-length unaltered CsnSN and its variants. The variants were constructed with the changes in the three predicted proteinase-binding regions: the N-terminus (variant N(12-13), G12A-G13A), beta-hairpin loop I (variant L(56-58), Q56G-T57G-V58G) and beta-hairpin loop II (variant L(106-107), P106G-W107G). The secreted CsnSNs were purified using sequential spiral cartridge ultrafiltration and DE-52 radial flow chromatography. The purified proteins were examined for papain- and cathepsin C-inhibition. The wild-type CsnSN, and variants N(12-13) and L(106-107) bound tightly to papain (K(i) < 10 pM), whereas mutation in the loop I reduced binding affinity 5700-fold (K(i) = 57 nM). On the other hand, the wild-type CsnSN bound to cathepsin C less tightly (K(i) = 100 nM). The mutation in the N-terminus or loop I reduced binding affinity by 16 (K(i) = 1.6 microM)- and 19-fold (K(i) = 1.9 microM), respectively, while mutation in loop II resulted in an ineffective cathepsin C inhibitor (K(i) = 14 microM). Collectively, these results suggest that the N-terminal G12-G13 residues of CsnSN are not essential for papain inhibition but play a role in cathepsin C inhibition; residues Q56-T57-V58 in the loop I are essential for both papain and cathepsin C inhibitions, and residues P106-W107 in the loop II are not important for papain inhibition but essential for cathepsin C inhibition. These results demonstrated that CsnSN variants have different effects toward different cysteine proteinases.

Animals↗

PubMed1998

CD44 isoforms, including the CD44 V3 variant, are expressed on endothelium, suggesting a role for CD44 in the immobilization of growth factors and the regulation of the local immune response.

Endothelium plays a central role in the regulation of site and inflammation specific leukocyte migration. Some of the mediators involved in leukocyte migration, such as chemokines, can bind to heparan sulfate on the endothelium resulting in immobilization near their sites of production. Because CD44 variants expressing V3 have been shown to carry heparan sulfate side chains and to interact through these side chains with heparan sulfate binding growth factors, we investigated the expression of CD44 variants on endothelium. We found a strong expression of V5, V7-8 and V10 CD44 variants and a weaker expression of V3 and V6 CD44 variants on endothelium by using immuno-histochemistry and by FACS analysis. Expression of CD44 V3 variants was confirmed at both the protein and mRNA levels by Western blotting and by reverse transcriptase-PCR respectively. Expression of CD44 variants was unaffected by IL-1beta, IL-8, TNFalpha, IFNgamma or IL-4 treatment, indicating either constitutive expression of these variants or involvement of other cytokines in their regulation.

Antibodies, Monoclonal↗

PubMedDate not supplied

HFE S65C variant is not associated with increased transferrin saturation in voluntary blood donors.

Two amino acid variants in the HFE gene, C282Y and H63D, have been reported in most cases of hereditary hemochromatosis. A recently discovered novel amino acid variant of HFE, namely S65C, has been implicated to be responsible for a mild form of iron overload. We determined genotypes of the HFE S65C variant in 230 voluntary blood donors with a transferrin saturation >45%, who did not carry the HFE C282Y variant. The control group consisted of 248 first time blood donors who had a transferrin saturation < 45%. We also determined genotypes of the HFE H63D variant in the two groups. For the HFE S65C variant, the frequency of the HFE C65 allele was 1. 7% and 2.2% in the high and low transferrin saturation groups, respectively (p = 0.65). In contrast, for the HFE H63D variant, the frequency of the HFE D63 allele was 24.8% and 14.7% in the high and low transferrin saturation groups, respectively (p = 0.0009). This study demonstrates no association of the HFE C65 allele with the phenotype of high transferrin saturation. The results do not support the use of DNA genotyping for the HFE S65C mutation in population screening studies for hemochromatosis.

Adult↗

PubMed1997

Complete primary structure of two splice variants of collagen XII, and assignment of alpha 1(XII) collagen (COL12A1), alpha 1(IX) collagen (COL9A1), and alpha 1(XIX) collagen (COL19A1) to human chromosome 6q12-q13.

Overlapping cDNA clones that encode the full-length human alpha 1(XII) collagen polypeptides were isolated. The long variant molecule cDNA of 9750 nucleotides (nt) contains a 9189-nt open reading frame encoding 3063 amino acid residues. The short variant molecule cDNA of 6258 nt contains a 5697-nt open reading frame encoding 1899 amino acid residues. At the amino terminus of each variant is a 24-residue signal peptide that is followed by the mature polypeptides of 3039 amino acid residues with a calculated molecular mass of 330,759 Da for the long variant and 1875 amino acid residues with a calculated molecular mass of 203,163 Da for the short variant polypeptide. The human collagen XII chains are predicted to have all the structural domains described for the molecules in chicken and mouse, including, fibronectin type III repeats, von Willebrand factor A domains, and two triple-helical domains similar to those of all the other collagen family members. The amino acid residue sequence of human alpha 1(XII) collagen showed 92% identity to the mouse chain and 78% identity to the chicken chain. The sequence of three peptide fragments of collagen XII isolated from human placenta was identical to the sequence predicted from the deduced cDNA sequence and confirms that the cDNA encodes human alpha 1(XII) collagen. An isolated genomic clone was used to map the locus of the COL12A1 gene to chromosome 6q12-q13, very close to the locus of the FACIT collagen genes COL9A1 and COL19A1. RT-PCR on a variety of cDNAs demonstrates that both variant transcripts appear in human amnion, chorion, skeletal muscle, small intestine, and in cell cultures of human dermal fibroblasts, keratinocytes, and endothelial cells. Only the small variant transcript is apparent in human lung, placenta, kidney, and a squamous cell carcinoma cell line. These results confirm the previous observations showing that collagen XII is found in collagen I-containing tissues.

Alternative Splicing↗

PubMed1995

Splice variants of CD44 in human cervical cancer stage IB to IIB.

Aberrant expression of the cell adhesion molecule CD44 has been detected in human tumors and the expression of specific CD44 isoforms (splice variants) has been shown to be associated with metastasis and poor prognosis in human malignancies. We used three different variant exon sequence-specific murine monoclonal antibodies to epitopes encoded by exon v5, exon v6, or exon v7-v8 of human variant CD44 to study the expression of CD44 splice variants by immunohistochemistry in human cervical cancer. One-hundred five patients with surgically treated squamous cell carcinomas of the cervix stages IB to IIB were included in the study. CD44 splice variants CD44v5, CD44v6, and CD44v7-8 were detected in 70, 67, and 26%, respectively. Tumors expressing exon v6 had significantly more often metastasized to the pelvic nodes (58 vs 79%, P = 0.04). Expression of exon v6 was significantly correlated with a greater probability of vascular space invasion (73 vs 50%, P = 0.04) and a significantly lower rate of inflammatory stromal reaction (48 vs 78%, P = 0.004). Patients suffering from tumors expressing splice variant CD44v6 showed poorer overall survival (P = 0.03). In cases with negative pelvic lymph nodes we found a poorer prognosis when tumors expressed CD44v6 (P = 0.01) or CD44v7-8 (P = 0.02). Among the investigated CD44 splice variants expression of exon v6 is the most promising prognostic marker in surgically treated cervical cancer.

Adult↗

PubMed1997

An approximately half set of histone genes is enough for cell proliferation and a lack of several histone variants causes protein pattern changes in the DT40 chicken B cell line.

Of the 44 chicken histone genes, 39 are located in a major histone gene cluster of 110 kb, the others residing in four separate regions. The 42 sequenced genes encode six H1 variants, three H2A variants, four H2B variants, two H3 variants, and one histone H4. To clarify the influence on cell functions of simultaneous deletion of an approximately half set of the genes and some of the variants, we generated homozygous chicken DT40 mutants by disruption of two allelic segments of 57 kb, containing the 21 genes, using gene targeting techniques. Analyses with antisense RNA probes common or specific for gene families H1, H2A, H2B, H3 and H4 indicated that the remaining members of each of the gene families were expressed more in the mutants than in DT40 cells, resulting in maintenance of constant steady-state levels of mRNAs. Two-dimensional polyacrylamide gel electrophoresis showed that in the mutants several cellular proteins newly appeared or increased, and some other proteins disappeared or decreased quantitatively. These results demonstrate that all the histone gene families have the inherent ability to compensate for the disruption of a fair number of their own constituents. Furthermore, some of the histone variants are involved in regulation of the expression of putative genes that encode the proteins that varied in mutant DT40 cells, this participation is not compensated for by any residual variant of the same histone subtype(s).

Animals↗

PubMed2001

Supporting the structural basis of prion strains: induction and identification of [PSI] variants.

The [PSI] genetic element, which enhances the nonsense suppression efficiency in the yeast Saccharomyces cerevisiae, is thought to be amyloid-like aggregates of the Sup35 protein, and to self-propagate by a prion-like mechanism. Analogous to strains of the mammalian prion, variants of [PSI], with different nonsense suppression efficiencies and mitotic stabilities, can be isolated from the same yeast genetic background. In the framework of the "protein-only" hypothesis, variants of prion are assumed to be distinct conformers of the same prion polypeptide. This study aims to provide further support for the structural basis of [PSI] variation. Three variants of [PSI] were induced and distinguished by a panel of 11 single point mutations of the Sup35 protein. The variant phenotypes are intrinsically associated with [PSI] elements, presumably structurally different amyloids, rather than produced from variations in the genetic background. Differential incorporation to [PSI] variants of a Sup35 point mutation as well as N and C-terminally truncated Sup35 fragments is further demonstrated in vivo, suggesting that distinct patches of amino acid residues are involved in the assembly of [PSI] variants. These results establish a method for [PSI] variant-typing and indicate that heritable variations of amyloid structures can be derived from the same polypeptide.

Alleles↗

PubMed2001

In-vitro selection of highly stabilized protein variants with optimized surface.

Thermostable proteins are of prime importance in protein science, but it has remained difficult to develop general strategies for stabilizing a protein. Site-directed mutagenesis based on comparisons with thermophilic homologs is rarely successful because the sequence differences are too numerous and dominated by neutral mutations. Here we used a method of directed evolution to increase the stability of a mesophilic protein, the cold shock protein Bs-CspB from Bacillus subtilis. It differs from its thermophilic counterpart Bc-Csp from Bacillus caldolyticus at 12 surface-exposed positions. To elucidate the stabilizing potential of exposed amino acid residues, six of these variant positions were randomized by saturation mutagenesis, the corresponding library of sequences was inserted into the gene-3-protein of the filamentous phage fd, and stabilized variants were selected by the Proside technique. Proside links the increased protease resistance of stabilized protein variants with the infectivity of the phage. Many strongly stabilized variants of Bs-CspB were identified in two selections, one in the presence of a denaturant and the other at elevated temperature. Several of them are significantly more stable than the naturally thermostable homolog Bc-Csp, and the best variant reaches Tm-Csp (the homolog from the hyperthermophile Thermotoga maritima) in stability. Remarkably, this variant differs from Tm-Csp at five and from Bc-Csp at all six randomized positions. This indicates that proteins can be strongly stabilized by many different sets of surface mutations, and Proside selects them efficiently from large libraries. The course of the selection could be directed by the conditions. In an ionic denaturant non-polar surface interactions were optimized, whereas at elevated temperature variants with improved electrostatics were selected, pointing to two different strategies for stabilization at protein surfaces.

Amino Acid Sequence↗

PubMed1993

Phenotypic and functional characterization of mouse attenuated and virulent variants of foot-and-mouth disease virus type O1 Campos.

A series of genetically related variants arising from a parental wild-type isolate of O1 Campos and its tissue culture adapted variant were differentiated by various cell culture markers (temperature sensitivity, plaque size, viral yield) and lethality in mice. These isolates were additionally characterized functionally and biochemically by examining poly(C) length, RNA synthesis, protein synthesis, and cell receptor binding. In primary bovine kidney cells, the virulent isolates had greater levels of protein synthesis, whereas in baby hamster kidney cells, the attenuated variant outproduced the wild-type parent. The tissue culture adapted variant had substantially greater ability to attach to cells than the parental wild type. The parental wild-type and the tissue culture-adapted variant were similarly neutralized by various sera against whole virus, but the parental wild type was less effectively neutralized by sera prepared from either full or truncated (variable region) bacterially expressed VP1 polypeptides. The capsid region of the genomes of both these variants was sequenced and a nucleotide substitution resulting in a change in amino acid 56 in VP3 was found. The nucleotide sequence change for the remaining two variants was that of the parental wild-type virus.

Animals↗

PubMed1994

Satellite tobacco mosaic virus sequence variants with only five nucleotide differences can interfere with each other in a cross protection-like phenomenon in plants.

The type strain of satellite tobacco mosaic virus (STMV) contains two major variants, designated type 5 (T5) and type 6 (T6), which can be easily distinguished by RNase protection analyses. Clones containing cDNA of representative T5 and T6 STMV genomes have only five single-base differences in the entire 1059-nucleotide genome, and RNA transcribed from each clone is highly infectious when inoculated onto tobacco plants. The different RNase protection assay patterns can be used as genetic markers to identify individual STMV variants and to follow the interactions of variants and their progeny during coinfections in plants. The study described here investigated the effects of coinoculation and various delayed inoculations of T5 and T6 variants on the composition of the progeny STMV populations in systemically infected tobacco tissues. When T5 and T6 STMV RNAs were coinoculated or inoculated with 1-hr delays, the progeny from individual plants most often contained a mixture of T5 and T6 genomes. However, when there was a 24-hr delay between inoculations, the balance of T5 and T6 components in the progeny populations shifted toward predominance of the first variant inoculated. With delays of 3 or 7 days only the first variant was evident in the progeny populations, indicating that established replication of one STMV variant interferes with replication of another in a manner similar to the cross protection phenomenon.

Helper Viruses↗

PubMed1995

Egg fluids and cells of the chorioallantoic membrane of embryonated chicken eggs can select different variants of influenza A (H3N2) viruses.

Growth of influenza viruses in embryonated eggs frequently results in the selection of virus variants with amino acid changes near the receptor-binding pocket of the hemagglutinin molecule, yet the mechanism by which this third form of influenza variation occurs (the other two being antigenic drift and shift) has not been clearly defined. Because egg-mediated variation might affect influenza vaccine and surveillance programs, we have initiated studies to determine the site(s) of variant virus selection within the embryonated egg. In this report we show that both the cells of the chorioallantoic membrane (CAM) and the fluids from embryonated chicken eggs are capable of selecting variant influenza viruses, but that these variants are distinct at the molecular level depending on the conditions of virus propagation. Serial passage of viruses in cells of the chorioallantoic membrane selects one set of variants which possess specific amino acid changes near the receptor binding pocket of the hemagglutinin molecule characteristic of viruses grown in embryonated eggs. However, passage of the same viruses in mammalian tissue culture cells supplemented with egg fluids selects a separate set of hemagglutinin variants also characteristic of viruses grown in eggs, yet at different residues from those observed following passage in CAM. These results suggest that two separate mechanisms may exist in the embryonated egg that lead to the selection of variant influenza viruses: one at the cellular level and another at the extracellular level.

Allantois↗

PubMed1996

Natural populations of woodchuck hepatitis virus contain variant precore and core sequences including a premature stop codon in the epsilon motif.

We have determined a consensus sequence and the type and the frequency of spontaneous sequence variations in the woodchuck hepatitis virus (WHV) precore gene and the 5' region of the core gene in 101 serum samples from 53 naturally WHV-infected woodchucks by polymerase chain reaction sequencing. Twenty of the 53 woodchucks were found to have variant sequences. Ten patterns of variant sequences were identified in these 20 animals. WHV sequences from 4 woodchucks had 1 nucleotide change, 3 had 2 nucleotide changes and 3 had 3 nucleotide changes. The nucleotide changes were not randomly distributed, but were limited to only 8 sites. Four sites were in the epsilon motif of the precore gene and four were in the 5' region of the core gene. Sixteen of the 53 (30%) woodchucks had precore sequence variants. All altered sites were analogous to previously described mutations in hepatitis B virus. There was a nucleotide change at nucleotide 2016 in codon 29 of the precore region that produced a stop codon in 4 animals. This site is analogous to a common hepatitis B virus e antigen mutation. The sequence from the initial blood samples from 3 of 4 animals with this stop codon producing variant appeared to be the consensus sequence; however, in later samples the variant occurred as a mixed infection with the consensus sequence. The mixed infections were chronic and the proportion of the variant sequence was maintained or increased in the course of infection. In the fourth animal only the variant was found and it persisted for over 14 months of infection. WHV appears to be a valuable model for the study of the structure and function of the hepadnavirus precore region.

Animals↗