Yasuhito Tanaka

Genomic and Molecular Evolutionary Analysis of a Newly Identified Infectious Agent (SEN Virus) and Its Relationship to the TT Virus Family

A new group of transmissible single-stranded (ss) DNA viruses (SENV) distantly related to the large TT virus (TTV) family was recently identified. Eight different SENV isolates have been found, some with an association with posttransfusion hepatitis. A phylogenetic analysis of near-complete open-reading frame 1, including conserved motifs and excluding recombinant regions, was performed. The analysis used TTV-like minivirus as an outgroup, to determine a root of the phylogenetic tree, and compared 8 SENV isolates, 6 prototype TTV isolates, and 7 TTV variants (including SANBAN, TUS01, PMV, and YONBAN). Four distinct clusters separated by a bootstrap value of 100% were observed. YONBAN isolates formed a distinct outer group, representing the earliest recognized phylogenetic divergence (group 1). Prototype TTV formed group 2, PMV formed group 3, and SENV, SANBAN, and TUS01 isolates formed group 4, the most recently evolved group. This taxonomic classification suggests that these circular ssDNA viruses probably evolved from a common ancestor virus.

Observation of positive selection within hypervariable regions of a newly identified DNA virus (SEN virus)1

To elucidate the evolution of SEN virus (SEN‐V), serial sequences of chronically SEN‐V‐infected patients were analyzed. In the hypervariable regions, non‐synonymous substitutions significantly predominated. This could be attributed to positive selection in evading immune surveillance of the hosts and to establish a persistent infection. On the basis of the sequences in the two open reading frames of SEN‐V DNA, the rate of synonymous substitutions was 7.32×10−4 per site per year. Since this rate is close to RNA viruses and higher than other DNA viruses, the SEN‐V might be replicated by machinery with poor or no proofreading function.

Prevalence of SEN Viruses among Injection Drug Users in the San Francisco Bay Area

SEN viruses (SENVs) are newly discovered bloodborne viruses that may play a role in liver disease. SENV strain prevalence was examined in a race/ethnicity-stratified sample of 531 injection drug users (IDUs) from the San Francisco Bay area. Weighted prevalences were as follows: SENV-A, 45.7%; SENV-C/H, 35.6%; and SENV-D, 10.3%. Infection was associated with a longer duration of injection drug use. SENV-A was more common in black subjects (adjusted odds ratio [OR(a)], 4.37; 95% confidence interval [CI], 2.65-7.21) and Hispanic subjects (OR(a), 2.30; 95% CI, 1.38-3.85) than in white and non-Hispanic subjects, and the pattern was similar for SENV-C/H. For SENV-D, prevalence was similar in black and white subjects, but lower in Hispanic subjects; infection was less common among women than men (OR(a), 0.32; 95% CI, 0.15-0.71) and more common among men with at least 1 recent male sex partner than among heterosexual men (OR(a), 7.05; 95% CI, 2.62-18.95). SENV strains are common among San Francisco Bay area IDUs, and prevalence varies demographically within this group.

Partial purification and properties of phosphatidylethanolamine methyltransferase system from mouse liver microsomes

PE(phosphatidylethanolamine) methyltransferase system converts PE to PC(phosphatidylcholine) through PME(phosphatidylmonomethylethanolamine) and PDME(phosphatidyldimethylethanolamine) by stepwise N-methylation using SAM(S-adenosylmethionine) as methyl donor. This enzyme system distributes widely from bacteria to mammalian organs (Bremer, 1969) and was recently found in various mammalian cultured cells in our laboratory (Maeda et al., 1981). We think this pathway could have important roles in the functions of biological membranes as proposed by Hirata and Axelrod (1980), since PE is a major phospholipid of mammalian cell membranes and its conversion to PC within the membranes could affect the environments of integrated membrane proteins, by changing a charge as well as fluidity of the lipid bilayers. The purification of this enzyme system has not, however, been made for over 20 years after its discovery, since the enzyme system is integrated into the membranes and very labile after solubilization. This paper will report solubilization and partial purification of this enzyme system from mouse liver microsomes and further describe some properties of this enzyme system.