Certain small GTP-binding proteins control the enzymatic activity of a family of closely related serine-threonine kinases known as mitogen-activated protein kinases (MAPKs). In turn, these MAPKs, such as p44 mapk and p42 mapk , referred to herein as MAPKs, and stressactivated protein kinases, also termed c-Jun N-terminal kinases (JNKs), phosphorylate and regulate the activity of key molecules that ultimately control the expression of genes essential for many cellular processes. Whereas Ras controls the activation of MAPK, we and others have recently observed that two members of the Rho family of small GTP-binding proteins, Rac1 and Cdc42, regulate the activity of JNKs. The identity of molecules communicating Rac1 and Cdc42 to JNK is still poorly understood. It has been suggested that Pak1 is the most upstream kinase connecting these GTPases to JNK; however, we have observed that coexpression of Pak1 with activated forms of Cdc42 or Rac1 diminishes rather than enhances JNK activation. This prompted us to explore the possibility that kinases other than Pak might participate in signaling from GTP-binding proteins to JNK. In this regard, a computer-assisted search for proteins containing areas of homology to that in Pak1 that is involved in binding to Rac1 and Cdc42 led to the identification of mixed lineage kinase 3 (MLK3), also known as protein-tyrosine kinase 1, as a potential candidate for this function. In this study, we found that MLK3 overexpression is sufficient to activate JNK potently without affecting the phosphorylating activity of MAPK or p38. Furthermore, we present evidence that MLK3 binds the GTP-binding proteins Cdc42 and Rac1 in vivo and that MLK3 mediates activation of MEKK-SEK-JNK kinase cascade by Rac1 and Cdc42. Taken together, these findings strongly suggest that members of the novel MLK family of highly related kinases link small GTP-binding proteins to the JNK signaling pathway.

Torque teno virus (TTV), currently classified into the family Circoviridae, genus Anellovirus, was first found in a patient with non-A-E hepatitis. TTV has a single stranded circular DNA of approximately 3.8 kb. TTVs are extraordinarily diverse, spanning five groups including SANBAN and SEN viruses. Torque teno mini virus (TTMV) with approximately 2.9 kb genome also has wide variants. Recently, two related 2.2- and 2.6-kb species joined this community. Recombinations between variants are frequent. This extensive TTV diversity remains unexplained; it is unclear how TTVs could be viable, and why they require such genetic variation. An unequivocal culture system is still not available. TTVs are ubiquitous in > 90% of adults worldwide but no human pathogenicity of TTV has been fully established. Epidemiological surveys need to specify the variants being studied and clinical targets, and must calibrate the sensitivity of the assay used. Potentially interesting observations include a higher viral load in patients with severe idiopathic inflammatory myopathies, cancer and lupus. Active replication was also found in infants with acute respiratory diseases. TTV/TTMV-related viruses were found in chimpanzees, apes, African monkeys and tupaias, and also in chickens, pigs, cows, sheep and dogs. Experimentally, rhesus monkeys were persistently infected by TTV, but only 1/53 chimpanzees. TTV transcribes three species of mRNAs, 3.0-, 1.2- and 1.0-kb in the ratio of 60:5:35. Recently, at least three mRNAs were shown in chicken anaemia virus. The genomic region -154/-76 contains a critical promoter. TTV seems to have at least three proteins; however, the definite functions of these proteins await further research work.

The ATL prevention program (AAP) in the Nagasaki Prefecture since 1987 consists of screening of pregnant women and asking the seropositives to refrain from breast-feeding. We screened approximately 90% of gravidas in the Prefecture and > 90% of the seropositive women agreed not to breast-feed. The maternal transmission rate dropped from approximately 20% to approximately 3%. PCR of cord bloods showed that 2.5% were PCR-positive. However, among formula-fed children, none of the cord-positives seroconverted, and none of the seropositives tested had been cord-positive. Breast-feeding for less than six months decreased the transmission rate significantly, but may have a higher transmission rate than the formula feeding.

No abstract

The sequence data (H. Okamoto et al., Hepatol. Res. 10:1–16, 1998) of a newly discovered single-stranded DNA virus, TT virus (TTV), showed that it did not have the terminal structure typical of a parvovirus. Elucidation of the complete genome structure was necessary to understand the nature of TTV. We obtained a 1.0-kb amplified product from serum samples of four TTV carriers by an inverted, nested long PCR targeted for nucleotides (nt) 3025 to 3739 and 1 to 216 of TTV. The sequence of a clone obtained from serum sample TA278 was compared with those registered in GenBank. The complete circular TTV genome contained a novel sequence of 113 nt (nt 3740 to 3852 [=0]) in between the known 3′- and 5′-end arms, forming a 117-nt GC-rich stretch (GC content, 90.6% at nt 3736 to 3852). We found a 36-nt stretch (nt 3816 to 3851) with an 80.6% similarity to chicken anemia virus (CAV) (nt 2237 to 2272 of M55918), a vertebrate circovirus. A putative SP-1 site was located at nt 3834 to 3839, followed by a TATA box at nt 85 to 90, the first initiation codon of a putative VP2 at nt 107 to 109, the termination codon of a putative VP1 at nt 2899 to 2901, and a poly(A) signal at nt 3073 to 3078. The arrangement was similar to that of CAV. Furthermore, several AP-2 and ATF/CREB binding sites and an NF-κB site were arranged around the GC-rich region in both TTV and CAV. The data suggested that TTV is circular and similar to CAV in its genomic organization, implying that TTV is the first human circovirus.