A Fully Annotated Genome Sequence of Human T-Cell Lymphotropic Virus Type 1 (HTLV-1)
Published Date: June 23, 2019
A Fully Annotated Genome Sequence of Human T-Cell Lymphotropic Virus Type 1 (HTLV-1)
Fernanda K. Barreto1, Thessika HA. Araújo1,2, Filipe F. Almeida Rego3, and Luiz CJ. Alcantara1*
1Oswaldo Cruz Foundation, Institute Gonçalo Moniz , Salvador, Bahia, Brazil
2Bahian School of Medicine and Public Health, Salvador, Bahia, Brazil
3Catholic University of Salvador, Salvador, Bahia, Brazil
*Corresponding author: Luiz Carlos Junior Alcantara, Oswaldo Cruz Foundation, Institute Gonçalo Moniz, Salvador, Bahia, Brazil, E-mail: email@example.com.
Citation: Barreto FK, Araújo THA, Rego FFA, Alcantara LC (2017) A Fully Annotated Genome Sequence of Human T-Cell Lymphotropic Virus Type 1 (HTLV-1). J Bioinf Com Sys Bio 1(1): 105.
In the next generation of genome sequencing, sequence annotation plays an important role with respect to genome evaluation. The aim of annotation is to identify key features in the genome, such as genes and their products. Although annotation tools are available and some sequence features have been published, annotation information for many complete and partial genomes of Human T-Cell Lymphotropic Virus Type 1 (HTLV-1) remains unavailable from GenBank. Sequence analysis is critical to the understanding of the pathogenesis of HTLV-1, and a well-annotated reference sequence is an essential component in this analysis. More accurate and complete information about the HTLV-1 genome can assist the scientific community in investigations on possible therapeutic and prophylactic vaccines, as well as aid studies on the pathogenesis of HTLV-1-associated diseases. Here we describe for the first time the complete nucleotide position annotation of the frequently used HTLV-1 reference sequence, ATK1 (accession number: J02029.1).
Keywords: HTLV-1; ATK1; Complete Genome; Annotation
Human T-cell lymphotropic virus type 1 (HTLV-1) is present throughout the world and it is estimated that 5–10 million individuals are infected . This retrovirus has been mainly linked to Adult T Cell Leukemia/Lymphoma (ATLL), Tropical Spastic Paraparesis/HTLV-associated myelopathy (HAM/TSP) and infective dermatitis [2–4].
One of the challenges faced by researchers in the development of an HTLV-1 vaccine is to determine why some individuals develop pathological processes, while others remain asymptomatic. Genomic studies have indicated that HTLV-1 mutations may be associated with infection outcome, yet the GenBank database contains relatively few complete genomes available [5–8]. In addition, the most used HTLV-1 genome (ATK1) is incomplete with regard to the start and end nucleotide position of each gene. ATK1 was the first human retrovirus genome described and to date has not been fully annotated . Here, we performed the complete nucleotide position annotation of the full ATK1 genome available at GenBank. We hope that this information will support future HTLV-1 research efforts by the scientific community.
To perform the complete nucleotide position annotation of the most used HTLV-1 genome (ATK1), this sequence was downloaded from GenBank (accession number: J02029.1) and all available features were recorded. Next, we identified in GenBank other complete and partial HTLV-1 sequences with some nucleotide position information, through the “HTLV-1 complete sequence; HTLV-1 and LTR; HTLV-1 and HBZ; HTLV-1 and p12; HTLV-1 and p30” keywords.
After downloading these sequences, Clustal X 2.0 software was used to align all sequences, including ATK1 [10,11]. The alignment was manually edited and the correct nucleotide positions of the HTLV-1 genes in the complete and partial sequences was analyze in relation to ATK1 sequence. The nucleotide position annotation of ATK1 was performed using Geneious R6 software . Finally, Universal Protein Resource (UniProt, www.uniprot.org) was used to confirm coding region annotations through the alignment of HTLV-1 protein sequences available in the UniProt and the ATK1 sequence translated based on our annotations . Figure 1 explains the workflow of ATK1 nucleotide annotation.
Figure 1: The workflow of ATK1 nucleotide position annotation. The ATK1 accession numbers is J02029.1. The accession numbers of the HTLV-1 complete and partial sequences downloaded are NC_001436, Y16487.2, U19949, JX184913.1 and KM436104.1.
Complete nucleotide annotations provide the scientific community with the necessary data to better interpret biological processes. In the case of HTLV-1, this information is particularly important since the literature is controversial with respect to the nucleotide position of each of the protein products, especially those produced by pX.
To establish a localization standard for the HTLV-1 genes and proteins, we analyzed the ATK1 sequence and performed the complete nucleotide annotation of this sequence. As shown in figure 2, the HTLV-1 genome is composed of genes gag, pol, env and the pX region, flanked by two Long Terminal Repeat (LTR) regions at both 5' and 3' ends. The gag precursor protein is cleaved into products. The pol gene encodes polymerase p95 (reverse transcriptase) and an integrase, although the sites of translation initiation have yet to be determined. A frameshift occurs at the 3' gag termination and the beginning of the pol gene, which encodes p14 (protease). The env precursor protein is also cleaved to generate two products: gp46 and gp21. The pX region contains four overlapping open reading frames (ORF) that encode regulatory and accessory proteins and an antisense mRNA that generates the basic leucine zipper (HBZ) protein and the isoform of HBZ (HBZ-SI). ORF-I produces the p12 protein, which can be further cleaved into p8 protein, while ORF-II produces two proteins: p13 and p30, with part of the p30 protein being coded by env. ORF-III and ORF-IV produce proteins p27 (Rex) and p40 (Tax), respectively, both also partially coded by env. The size of this genome is approximately 9 kilobase (kb) and the start and end nucleotide positions of each gene are described below in Table 1.
Figure 2: The fully annotated genome of human T-cell lymphotropic virus type 1 (HTLV-1). (The complete HTLV-1 genome is represented as a box. The LTR promoter regions and the genes encoded by sense mRNA are shown in different colors. Each protein is represented by a line with a color specific to its corresponding gene. HBZ and HBZ-SI are encoded by an antisense mRNA, represented by a dotted line. Proteins labeled with asterisks (*) are encoded by more than one gene).
Table 1: Nucleotide positions of HTLV-1 genes in the ATK1 sequence (accession number: J02029.1). (The sites of reverse transcriptase (p95) and integrase translation initiation have not been determined; LTR = long terminal repeat).
The RefSeq database of GenBank suggests another sequence as reference (accession number: NC_001436). However, most of HTLV-1 papers used the ATK1 as reference sequence in their analysis [14–16]. Nevertheless, both of these sequences do not have information about all the HTLV-1 products, as p14, p12, p8, p30, p13 and HBZ. Therefore, our complete results can be used as a reference for the alignment and annotation of other HTLV-1 genomes.
The present study attempted to perform a complete nucleotide annotation of the most used HTLV-1 complete genome, ATK1. There are many questions that remain to be answered in the field of HTLV-1 research, and we hope that these data will assist other investigations carried out by the scientific community.
Availability of Data and Material
All sequences are available in the GenBank database (accession numbers: J02029.1; NC_001436; Y16487.2; U19949; JX184913.1; KM436104.1).
All authors wrote, read and approved the final manuscript.
Conflicts of Interest
The authors declare that they have no competing interests.
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Copyright: © 2017 Barreto FK, et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.