Synthesis of 2'-deoxy-6,3'-methano-cyclo-pyrimidine nucleosides

The nucleophilic attack of lithiated pyrimidines to a suitably-protected 3-ketosugar, afforded the 3-branched sugar stereospecifically, followed by intramolecular glycosylation to give 6,3'-methano-cyclo-pyrimidine nucleosides. The 2'-deoxygenation was achieved by sequential protection, deprotection and radical reduction.     

Molecular basis for the spontaneous generation of colonization-defective mutants of Streptococcus mutans

Spontaneous mutants of Streptococcus mutans GS-5 defective in sucrose-dependent colonization of smooth surfaces are generated at frequencies above the spontaneous mutation rate. Southern blot analysis of such mutants suggested rearrangement of the genes coding for glucosyltransferase (GTF) activity. Two strain GS-5 homologous tandem genes, gtfB and gtfC, coding for GTF-I and GTF-S activities respectively, were demonstrated to undergo recombination when introduced into recombination-proficient Escherichia coli transformants. However, the two genes were quite stable when transformed on a single DNA fragment into a recA mutant of E. coli. The DNA fragment coding for GTF activity from one S. mutans colonization-defective mutant, SP2, was isolated and shown also to have undergone recombination between the gtfB and gtfC genes, resulting in reduced GTF activity. These results are discussed relative to the in vivo generation of colonization-defective mutants in cultures of S. mutans.     

A model of neural network extracting binocular parallax

A model of neural network extracting binocular parallax is proposed. It is a multilayered network composed of analog threshold elements. Three types of binocular neurons are included in this model. They are binocular simple neurons, binocular gate neurons and binocular depth neurons. The final layers of this model consist of elements which correspond to the binocular depth neurons. The performance of the model has been simulated on a digital computer. The results of the computer simulation show that every element of this model acts like neurons found in cat's and monkey's visual system and this model extracts binocular parallax caused by simple line components satisfactorily.     

Antigenic variation among Sendai virus strains detected by monoclonal antibodies

Thirteen strains of Sendai virus isolated from various sources in the 1950's and after 1976 were compared for their reactivities with monoclonal antibodies prepared against the prototype strain MN of Sendai virus. Results revealed that while the 5 strains isolated in the 1950's reacted with all the monoclonal antibodies as the prototype strain did, the 2 strains isolated in 1976 and 1978 did not react with an F-specific monoclonal antibody, and the other 6 strains isolated after 1978 lacked reactivity with an HN-specific monoclonal antibody.     

Deficiencies in suppressor T cell activity seen in patients with active systemic lupus erythematosus are due to the dilution of normally functioning suppressor T cells by nonsuppressor T cells

Concanavalin A (Con A)-activated T lymphocytes from patients with active, but not inactive, systemic lupus erythematosus (SLE) failed to express normal suppressor activity, regardless of the phenotype of CD4+ or CD8+. Con A-activated CD4+ or CD8+ T lymphocytes from the SLE patients and from normal controls were further separated into two populations, using the autologous erythrocyte rosette technique. One population very rich in cells capable of forming rosettes with autologous erythrocytes from the active patients showed the same degree of suppressor activity, as did that from normal controls; the CD4+ or CD8+ population poor in autorosetting cells derived from Con A-activated T lymphocytes from both the controls and patients did not express suppressor activity. Moreover, when autorosetting T cells from the active patients and nonrosetting cells from the same patients were mixed at a normal ratio (4:6), normal suppressor activity could be restored. It was notable that the frequency of autorosette-forming cells was markedly reduced in the Con A-activated T lymphocytes from the active, but not inactive, SLE patients, regardless of the phenotype of CD4+ or CD8+. These findings indicate the presence of a normally functioning suppressor T cell population in patients with active SLE. It seems that the lack of suppressor T cell function in patients with active SLE is due to the dilution of a few normal suppressor T cells by large numbers of nonsuppressor T lymphocytes.     

Synthesis of 5'-phosphatidylnucleosides by phospholipase D-catalyzed transphosphatidylation

Phospholipase D from Streptomyces effectively catalyzed the transfer reaction of the phosphatidyl residue from phosphatidylcholine to the 5'-hydroxyl group of nucleosides. A variety of 5'-phosphatidylnucleosides were prepared by this reaction in high yields. Some of them showed marked antitumor activities in mice.