A small portion of the cytosine residues in the DNA of higher eukaryotes as well as in that of many lowe eukaryotes if methylated. The resulting 5-methylcytosine residues occur in specific in the DNA, usually adjacent to guanine residues on the 3' side. This methylation of eukaryotic DNA has been proposed to function in many ways, including control of transcription, maintenance of chromosome structure, repair of DNA, establishment of preferred sites for mutation, oncogenic transformation, and, in certain systems, protection of DNA against enzymatic degradation.

SEN virus (SEN-VAfter cloning of the hepatitis C virus (HCV) 1 and development of sensitive serologic and molecular assays for this pathogen, a dramatic decline in the incidence of transfusionassociated hepatitis occurred. 2,3 However, approximately 10% of transfusion-associated hepatitis cases 4 and 20% of community-acquired hepatitis cases 5 do not have a defined etiology suggesting the existence of additional causative agents. Hepatitis G virus (HGV), 6 also known as GB virus C (GBV-C), 7 was initially suggested as a causative agent of non-A to E hepatitis, but this was not confirmed in further studies. [8][9][10] The originally described TT virus (TTV), discovered in 1997 by representational difference analysis, was detected in 3 of 5 cases of transfusion-associated hepatitis and was proposed as a potential cause of non-A to E hepatitis. 11 Using TTV primers identical to those reported, non-A to E hepatitis cases and controls in the NIH prospective series were tested but no association with transfusion-associated hepatitis was found. 12 Subsequently, primers to more conserved regions of the TTV genome were used in studies in Japan, and the agent was found in greater than 90% of Japanese blood donors. 13 This further diminished the likelihood that TTV was the cause of transfusion-associated hepatitis and precluded the possibility of a practical screening assay. Other studies have also confirmed the high prevalence of TTV and its lack of association with transfusion-associated hepatitis. 14,15 Recently, a novel DNA virus designated SEN virus (SEN-V) was discovered in the serum of an intravenous drug abuser also infected with human immunodeficiency virus. 16,17 SEN-V was initially described as a single-stranded DNA virus of approximately 3,800 nucleotides. 16 Phylogenetic analysis of SEN-V has shown the existence of 8 strains. 18 Although structurally similar to TTV, SEN-V has less than 55% sequence homology and less than 37% amino acid homology with the TTV prototype. 18 Preliminary studies of SEN-V variants were conducted by Dr. Primi (DiaSorin Inc., Brescia, Italy). The prevalence of 5 SEN-V strains (A, B, H [former C], D, and E) and a consensus sequence designated total SEN-V were measured in various donor and patient populations. It was shown that measuring total SEN-V was not practical because the prevalence in donors was 13% and the rate in all transfused populations exceeded 70%. SENV-B was also excluded as a useful screening assay because it was present in 10% of donors and only 8% of patients with transfusion-associated non-A to E hepatitis. SENV-A and SENV-E were found in low prevalence in donors, but did not appear to be associated with non-A to E hepatitis. In contrast, SENV-D and SENV-H had favorable prevalence ratios being found in less than 1% of donors and more than 50% of transfusion-associated non-A to E cases. These initial polymerase chain reaction (PCR) data were confirmed by cloning and sequencing which showed that SENV-D and SENV-H sequences were found in a high proportion of non-A to E ...

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.

Sodium bisulfite is a mutagen which can specifically deaminate more than 96% of the cytosine residues in single-stranded DNA via formation of a 5,6-dihydrocytosine-6-sulfonate intermediate. Under the same reaction conditions, only 2-3% of the 5-methylcytosine (m5Cyt) residues in single-stranded XP-12 DNA, which has 34 mole% m5Cyt, was converted to thymine (Thy) residues. In contrast, at the deoxynucleoside and free base levels, the same treatment with bisulfite and then alkali converted 51% and > 95%, respectively, of the m5Cyt to the corresponding Thy derivatives. However, the rate of reaction of m5Cyt and its deoxyribonucleoside was much slower than that of the analogous quantitative conversion of cytosine or deoxycytidine to uracil or deoxyuridine, respectively. The much lower reactivity of m5Cyt and its derivatives compared to that of the unmethylated analogs is primarily due to a decrease in the rate of formation of the sulfonate adduct.

The existence of the newly discovered SEN virus (SENV) was investigated in 379 Japanese patients with liver diseases and in 277 blood donors, to determine whether SENV is associated with non-A-E hepatitis. SENV DNA was detected by seminested polymerase chain reaction, with primers directed to 2 SENV strains: SENV-H and SENV-D. SENV was detected in 7 (32%) of 22 patients with fulminant hepatitis, in 15 (17%) of 86 patients with acute hepatitis, in 38 (27%) of 139 patients with chronic hepatitis, in 29 (31%) of 93 patients with liver cirrhosis, in 5 (33%) of 15 patients with autoimmune hepatitis, in 11 (46%) of 24 patients with primary biliary cirrhosis, and in 27 blood donors (10%). Infection occurred more frequently in patients with liver diseases than in blood donors; however, there were no significant differences in SENV-positive rates between patients with non-A-C hepatitis and those with acute or chronic hepatitis due to known hepatitis virus or nonviral liver disease. This study did not suggest SENV as a possible causative agent of non-A-C hepatitis.