Immune response genes of the murine major histocompatibility complex encode cell-surface glycoproteins that are expressed predominantly on B cells and macrophages and regulate immune responsiveness by restricting antigen recognition by T cells. The two classes of immune response molecule, termed I-A and I-E, are each comprised of two polymorphic chains (alpha and beta), and nucleotide sequence analysis of genomic or cDNA clones has revealed that most of the amino acid differences between allelic I-A alpha or beta chains occur in the first extracellular domain. The mutant mouse strain B6.C-H-2bm12 (bm12), which differs from its parental strain C57BL/6 (B6) at the I-A beta locus, exhibits an immune response profile markedly different from that of B6. Here we present the nucleotide sequence of the mutant bm12 I-A beta gene. Sequence comparison within the coding regions reveals three productive nucleotide differences between the I-A beta genes of B6 and bm12 mice, all three differences occurring within a stretch of 14 nucleotides in the exon encoding the first extracellular domain. The clustered nature of the bm12 mutation, as well as the specific amino acid changes it engenders, suggest a possible mechanism for the generation of polymorphism in class II antigens.

The polymorphism of immune response genes plays a critical role in determining the immune capabilities of a particular individual. The molecular nature of this polymorphism was studied by examining the structure of the coding portions of three alleles of the I-A beta chain gene, an immune response gene whose protein product constitutes a subunit of the I-A molecule. Comparison of the I-A beta chains encoded by these alleles revealed an amino acid sequence divergence of 5 to 8 percent. The differences were found to be a series of short alterations clustered in the amino terminal half of the polypeptide.

We have investigated the structure of the photosynthetic membrane in a mutant of barley known to lack a chlorophyll-binding protein. This protein is thought to channel excitation energy to photosystem II, and is known as the "light-harvesting chlorophyll-protein complex." Extensive stacking of thylakoids into grana occurs in both mutant and wild-type chloroplasts. Examination of membrane internal structure by freeze-fracturing indicates that only slight differences exist between the fracture faces of mutant and wild-type membranes. These differences are slight reductions in the size of particles visible on the EFs fracture face, and in the number of particles seen on the PFs fracture face. No differences can be detected between mutant and wild-type on the etched outer surface of the membrane. In contrast, tetrameric particles visible on the etched inner surface of wild-type thylakoids are extremely difficult to recognize on similar surfaces of the mutant. These particles can be recognized on inner surfaces of the mutant membranes when they are organized into regular lattices, but these lattices show a much closer particle-to-particle spacing than similar lattices in wild-type membranes.Although several interpretations of these data are possible, these observations are consistent with the proposal that the light-harvesting chlorophyll-protein complex of photosystem II is bound to the tetramer (which is visible on the EFs face as a single particle) near the inner surface of the membrane. The large tetramer, which other studies have shown to span the thylakoid membrane, may represent an assembly of protein, lipid, and pigment comprising all the elements of the photosystem II reaction. A scheme is presented which illustrates one possibility for the integration of the light reaction across the photosynthetic membrane.The light reaction of photosynthesis is localized within the thylakoid membranes found in higher plants and green algae. The structure of these membranes is exceedingly complex, but now seems to be understood in general terms. At least two types of particles exist within the membrane, and can be visualized by the freeze-fracture technique (10,14,22). The larger of these particles is found principally in stacked (grana) regions of the chloroplast (14, 33, footnote 1), spans the thylaStaehelin, L. A. 1976. Reversible particle movements associated with unstacking and restacking of chloroplast membranes in vitro.

Neuropeptide tyrosine (neuropeptide Y, NPY) is a potent vasoconstrictor with a wide distribution in the central and peripheral nervous systems. Here we show that high levels of rat NPY mRNA are also found in peripheral blood cells, bone marrow, lung, and spleen. Furthermore, radioimmunoassay revealed high levels of NPY-like peptide in these tissues. In mice, the levels of splenic NPY mRNA and immunoreactive peptide differed extensively between strains and were greatly elevated in several strains (NZB, NZBxW, and BXSB) that develop a disease resembling human systemic lupus erythematosus. Like the rat, the NZB mouse showed a high content of NPY mRNA in peripheral blood cells and bone marrow. Immunohistochemical staining revealed NPY-like immunoreactivity in large cells morphologically identifiable as megakaryocytes in rat bone marrow and in the spleen of the NZB mouse strain. Expression of NPY mRNA in megakaryocytes in rat bone marrow and NZB mouse spleen was confirmed by in situ hybridization. These results indicate that NPY is synthesized in megakaryocytes, implying that NPY can be released from platelets and function as a vasoconstrictor during blood-vessel damage. In addition, the increase in splenic NPY in certain autoimmune mouse strains adds to the list of abnormalities associated with these strains.Neuropeptide Y (NPY), first isolated from pig brain by Tatemoto et al. (1), is abundant and widespread in the mammalian nervous system (2-7). In addition, NPY-like immunoreactivity has been found in chromaffin cells of the adrenal gland (8). The colocalization of NPY with catecholamines in numerous peripheral and central neurons (2, 9), together with its prejunctional inhibitory effects on transmitter release and its vasoconstrictor actions, suggests a function for NPY as a neurotransmitter and/or neuromodulator (2, 10). The structure of the NPY precursor has been deduced from a human cDNA clone (11) and from the rat gene (12). The rat NPY precursor consists of 98 amino acids including a signal peptide of 29 amino acids (12). At least two proteolytic processing sites are found within the NPY precursor; cleavage at these sites generates the 36 amino acid-long mature NPY peptide and a 30 amino acid-long carboxylterminal peptide (12). The human (13) and rat (12) genes are highly homologous and each consists of four exons, with almost the entire mature peptide encoded in the second exon.In accordance with the widespread distribution of NPYlike immunoreactivity in the brain (3, 4, 6, 7), Larhammar et al. (12) recently showed that NPY mRNA is present throughout the rat brain, with particularly high levels in the cerebral cortex and olfactory bulb. In rat peripheral organs, high levels of NPY mRNA were detected in the adrenal gland, heart, and spleen (12). The high level of NPY mRNA in rat spleen was unexpected, since no neuronal cell bodies are known in this organ, although many NPY-containing nerve terminals exist (2,14). In this paper we show that rat and mouse NPY mRNA and peptide are synthesized in megakar...

Summary. Mouse