Analyses of TT virus full-length genomic sequences.

Abstract

Since the identification of TT virus, only one full-length and two near full-length sequences representing a single subtype of the virus have been reported. In order to understand further the nature of the TT virus genome, nine of the most divergent TT virus sequences have been extended to full-length or near full-length. Phylogenetic analysis demonstrated that these sequences represent three distinct TT virus genotypes and two subtypes. A high degree of nucleotide sequence variability (approximately 30 %) was observed across the genomes with several significantly more divergent regions. Three conserved ORFs were identified, none of which shared significant amino acid sequence identity to sequences present in public databases. Additionally, sequence motifs, such as those necessary for protein translation and for rolling circle replication, were found to be partially conserved between all TT virus isolates.

TT Virus Infection in Patients on Peritoneal Dialysis in Taiwan

“…Sequence alignment of several near full-length TTV genomes revealed the presence of three conserved open reading frames and sequence motifs consistent with a rolling circle mode of replication. [13] Sequence analysis confirms that the TTV genome contains a high degree of genetic variability and can be classified into at least six major genotypes and several subtypes. [14] The genotypespecific pathogenicity of TTV remains unclear.…”

Extensive Homologous Recombination among Widely Divergent TT Viruses

“…While the role played by mutation has long been considered, it is becoming increasingly apparent that recombination also plays a key role in the evolution of many virus groups (19,24). The recent availability of several full-length TTV sequences (3,6,10,11,16), along with evidence for mixed infection by multiple genetic types (2,4,17,21), prompted this investigation into whether recombination might also play a role in the evolution of TTV.…”

“…While the role played by mutation has long been considered, it is becoming increasingly apparent that recombination also plays a key role in the evolution of many virus groups (19,24). The recent availability of several full-length TTV sequences (3,6,10,11,16), along with evidence for mixed infection by multiple genetic types (2,4,17,21), prompted this investigation into whether recombination might also play a role in the evolution of TTV.A total of 15 full-length or near-full-length TTV genomes with the following isolate names (accession numbers) were collected from GenBank: TA278 (AB017610) (16); GH1 (AF122913) (11); TUS01 (AB017613) (16); SAN-BAN (AB025946) (6); JA20 (AF122914), JA9 (AF122915), JA10 (AF122919), JA4 (AF122917), JA1 (AF122916), JA2B (AF122918), US32 (AF122921), and US35 (AF122920) (3); and BDH1 (AF116842), TTVCHN1 (AF079173), and TTVCHN2 (AF129887). The sequences were aligned using CLUSTAL W (23) and adjusted by hand.…”

Aspectos patológicos, imunológicos e propriedades moleculares do TT vírus

“…A região codificadora possui dois principais genes codificadores de proteínas open reading frame (ORF1 e ORF2), de 770 e 150 aminoácidos respectivamente (13) , e em alguns isolados há também uma pequena ORF adicional (ORF3) com capacidade para codificar 57 aminoácidos (8) (Figura). O produto da região ORF1 tem elevada proporção (aproximadamente 40%) de resíduos de arginina nos primeiros cem aminoácidos aminoterminais (24) , possui diferentes tipos de 30% um do outro, sendo que tais genótipos são classificados em quatro grupos filogenéticos principais, como demonstrado na Tabela.…”

“…O TTV é altamente heterogêneo, em contraste com a maioria dos vírus DNA. A divergência se encontra bem elevada na região central da ORF1, onde existem regiões hipervariáveis que podem levar a mais de 70% de diversidade no aminoácido, porém a região UTR desse vírus é bem conservada (8,23) .…”