Analysis of T-cell subsets in rejection of Kb mutant skin allografts differing at class I MHC

The T-cell subpopulations which initiate and mediate tissue allograft rejection remain controversial. In the present study we attempted to identify the phenotype and function of the T-cell subset(s) primarily responsible for the rejection of skin allografts differing at a single class I locus in the major histocompatibility complex (MHC). We found that the rejection rates by B6 mice (H-2b) of four different class I mutant (Kbm) skin allografts form a distinct hierarchy. This hierarchy correlates strikingly and uniquely with the relative precursor frequencies of Lyt2+ interleukin-2-secreting T-helper cells reactive against the various Kbm mutants. To investigate the role of Lyt2+ T cells in the rejection of class I-disparate skin allografts directly, H-2b nude mice were engrafted with Kbm skin allografts and then reconstituted with L3T4+ or Lyt2+ T-cell subpopulations from syngeneic H-2b mice. Lyt2+ T cells were observed to be both necessary and sufficient for the rejection of class I-disparate Kbm skin allografts, whereas L3T4+ T cells were neither necessary nor sufficient. These results identify the Lyt2+ interleukin-2-secreting T-cell subset as the critical cell type determining the rejection rate of class I-disparate Kbm skin allografts.     

The Tetrahymena ribozyme acts like an RNA restriction endonuclease

A shortened form of the Tetrahymena self-splicing ribosomal RNA intervening sequence acts as an endoribonuclease, catalysing the cleavage of large RNA molecules by a mechanism involving guanosine transfer. The sequence specificity approaches that of the DNA restriction endonucleases. Site-specific mutagenesis of the enzyme active site alters the substrate sequence specificity in a predictable manner, so that endoribonucleases can be synthesized to cut at a variety of tetranucleotide sequences.     

Loss of a Harvey ras allele in sporadic Wilms' tumour

Genomic changes within chromosome band 11p13 appear to have a role in the initiation of Wilms' tumour. The human Harvey ras oncogene, c-Ha-ras 1, has been located by Jhanwar et al. immediately adjacent to this region at band 11p14 .1, although several groups have assigned the gene more distally at band 11p15 . We have examined tumour DNA from two cases of sporadic Wilms' tumour, and report here that in both cases one of the two constitutional c-Ha-ras 1 alleles was absent. One tumour had a reciprocal translocation between the short arm of chromosome 11 (at band 11p13), and the long arm of chromosome 12, with no visible loss of chromosomal material. The loss of a c-Ha-ras 1 allele in association with this translocation indicates that a submicroscopic deletion had occurred. The resulting hemizygosity may have had a role in tumour initiation. Our results indicate that the c-Ha-ras 1 gene and the 'Wilms' tumour locus' may be in close proximity. It would, therefore, be premature to exclude the possibility that these two sites are functionally related.     

Effect of 5-hydroxytryptamine antibodies on pigment migration in the erythrophores of the fiddler crab,Uca pugilator: Further evidence for 5-hydroxytryptamine as a neurotransmitter that stimulates release of red pigment-dispersing hormone

Summary 5-Hydroxytryptamine (5-HT) antibodies inhibit red pigment dispersion in the fiddler crab,Uca pugilator. This observation supports the hypothesis that 5-HT stimulates release of red pigment-dispersing hormone.The 5-HT antibody preparation was a generous gift from Dr S. Spector, Roche Institute of Molecular Biology, Nutley, New Jersey.     

Molecular structure of r(GCG)d(TATACGC): a DNA--RNA hybrid helix joined to double helical DNA

The molecule r(GCG)d(TATACGC) is self-complementary and forms two DNA--RNA hybrid segments surrounding a central region of double helical DNA; its molecular structure has been solved by X-ray analysis. All three parts of the molecule adopt a conformation which is close to that seen in the 11-fold RNA double helix. The conformation of the ribonucleotides is partly determined by water molecules bridging between the ribose O2' hydroxyl group and cytosine O2. The hybrid-DNA duplex junction contains no structural discontinuities. However, the central DNA TATA sequence has some structural irregularities.     

Genetic variation at the alcohol dehydrogenase locus inDrosophila melanogaster: A third ubiquitous allele

Summary A 3rd allele at theAdh locus,Adh ^FCh.D., has been found at polymorphic frequencies in natural populations ofD. melanogaster. The ADH-FChD enzyme has properties distinct from those of the 2 more common forms of ADH. TheAdh polymorphism should now be analyzed as a triallelic system.