Antimutagenic unusual amino acids from plants

Five unusual amino acids were identified as antimutagens against spontaneous mutation of Salmonella typhimurium TA100: L-azetidine-2-carboxylic acid (1) from Liliaceae plants, alpha-(methylenecyclopropyl)glycine (2) from Litchi chinensis seeds, and 2-amino-4-methylhex-5-ynoic acid (3), hypoglycin A (4), and (2S,4R)-2-amino-4-hydroxyhept-6-ynoic acid (5) from Euphoria longana seeds. The absolute stereochemistry of 5 was determined by its chiral synthesis from L-allylglycine, proving that 5 is the C-4 epimer of the amino acid previously isolated from dried longan seeds.     

Duplications of a mutated simian virus 40 enhancer restore its activity

Enhancers are cis-acting control elements which can stimulate at a distance the activity of a variety of eukaryotic promoters. First identified as a repeated 72 base pair (bp) sequence upstream of the simian virus 40 (SV40) early gene promoter, enhancers have since been shown to be associated with numerous other viral and cellular genes. Although there are no strong homologies between the sequences of different enhancers, a number of short and degenerate consensus sequences have been identified, including the 'core' element GTGGA/TA/TA/TG and stretches of alternating purines and pyrimidines which may have the potential to form left-handed Z DNA. To study the functional significance of two alternating purine and pyrimidine sequences in the SV40 enhancer, we have introduced various combinations of point mutations into a modified SV40 enhancer which contained only one copy of the 72 bp element (W.H., Y.G., A. Nordheim and A. Rich, unpublished results); one of these combinations impaired both the activity of the enhancer and growth of SV40. We describe here the structure of 18 revertants of this mutant and suggest that in each of the 18 revertants, the defects of the original mutant have been overcome by simple tandem duplications in the enhancer region, all of which include the 'core' element.     

Six unidentified reading frames of human mitochondrial DNA encode components of the respiratory-chain NADH dehydrogenase

The products of six unidentified reading frames of human mitochondrial DNA are precipitated from a mitochondrial lysate by antibodies against highly purified native beef heart NADH-ubiquinone oxidoreductase (complex I). These products are enriched greatly in a human submitochondrial fraction enriched in NADH-Q1 and NADH-K3Fe(CN)6 oxidoreductase activities. We conclude that the six reading frames encode components of the respiratory-chain NADH dehydrogenase.     

Induction of calcium currents by the expression of the alpha 1-subunit of the dihydropyridine receptor from skeletal muscle

The dihydropyridine (DHP) receptor purified from skeletal muscle comprises five protein subunits (alpha 1, alpha 2, beta, gamma and delta) and produces Ca2+ currents that are blocked by DHPs. Cloning of the alpha 1- and alpha 2-subunits, the former affinity-labelled by DHP, has shown that the alpha 1-subunit is expressed in skeletal muscle alone, whereas the alpha 2- and delta- subunits are also expressed in other tissues. Although the transient expression of the alpha 1-subunit in myoblasts from dysgenic mice (but not in oocytes) has been demonstrated, the use of these expression systems to determine the function of the alpha 1- subunit is complicated by the presence of endogenous Ca2+ currents, which may reflect the constitutive expression of proteins similar to the alpha 2-, beta-, gamma- and/or delta-subunits. We therefore selected a cell line which has no Ca2+ currents or alpha 2- subunit, and probably no delta-subunit for stable transformation with complementary DNA of the alpha 1- subunit. The transformed cells express DHP-sensitive, voltage-gated Ca2+ channels, indicating that the minimum structure of these channels is at most an alpha 1 beta gamma complex and possibly an alpha 1- subunit alone.     

Myosin I is located at the leading edges of locomoting Dictyostelium amoebae

Movement of a eukaryotic cell along a substrate occurs by extension of lamellipodia and pseudopodia at the anterior and retraction at the posterior of the cell. The molecular and structural mechanisms of these movements are uncertain. Dictyostelium discoideum contains two forms of myosin. Here we show by immunofluorescence microscopy that non-filamentous myosin I occurs at the leading edges of the lamellipodial projections of migrating Dictyostelium amoebae, which are devoid of myosin II, whereas filamentous myosin II is concentrated in the posterior of the cells. On the basis of these locations of the two forms of myosin and their known biochemical and biophysical properties, we suggest that actomyosin I may contribute to the forces that cause extension at the leading edge of a motile cell, while the contraction of actomyosin II at the rear squeezes the cell mass forward. Myosin I isozymes might have similar roles in metazoan cells, for example at the leading edges of neuronal growth cones, and in the extension of lamellipodia and pseudopodia of leukocytes, macrophages and fibroblasts.     

Multiple endocrine neoplasia type 1 gene maps to chromosome 11 and is lost in insulinoma

Multiple endocrine neoplasia type 1 (MEN-1) is a predisposition to hyperplasia of the parathyroid glands, and to hyperplasia or tumours of the anterior pituitary and the endocrine pancreas, and is inherited as an autosomal dominant trait. Here we map the MEN-1 locus to chromosome 11 by family studies, and demonstrate tight linkage with the human muscle phosphorylase gene. By comparing constitutional and tumour tissue genotypes of insulinomas from a pair of brothers who had inherited MEN-1 from their mother, we have shown that oncogenesis in these cases involves unmasking of a recessive mutation at this locus.     

Hepatic phosphatidylcholine synthesis in deficiency of lysine and threonine: effect of malathion

Summary Rats fed on a rice diet deficient in lysine and threonine showed increased activities of CDP-Choline pathway enzymes and incorporation of (methyl-³H)-choline into hepatic microsomal phosphatidylcholine, compared to rats fed on the same diet supplemented with lysine and threonine. However, the amount of microsomal phosphatidylcholine was significantly decreased in rats fed a deficient rice diet. These results suggest an enhanced phosphatidylcholine catabolism in rats fed on a rice diet deficient in lysine and threonine. Malathion administration reduced the amount of phosphatidylcholine in all the groups.     

Identification of a receptor for protein import into chloroplasts and its localization to envelope contact zones

An anti-idiotypic antibody approach was used to identify an integral membrane protein of the chloroplast envelope as a receptor for protein import into the chloroplast stroma. The import receptor is found in contact sites between the outer and inner membrane of the chloroplast envelope.     

Diversity of gamma delta T-cell receptors on murine intestinal intra-epithelial lymphocytes

The search for the genes encoding the T-cell receptor (TCR) alpha- and beta-subunits revealed a third gene gamma which shares with the alpha- and beta-genes several properties including somatic rearrangement. This gene, together with a fourth rearranging gene delta, encodes a second type of T-cell receptor, TCR gamma delta. Although TCR gamma delta-bearing T cells constitute a relatively minor subpopulation in the thymus and in peripheral lymphoid organs, they are the major lymphocytes of epidermis (dendritic epidermal cells or DEC) and of intestinal epithelium (intestinal intraepithelial lymphocytes or IEL) in mice, suggesting that at least some gamma delta T cells are important in the surveillance of a variety of epithelia. It was recently reported, however, that the TCR gamma delta on DEC has essentially no structural diversity, implying that the putative ligand is monomorphic. As this finding, if generally applicable, poses severe restrictions on the origin of the ligand, we investigated the diversity of the TCR on the second major epithelium-associated gamma delta T cells, namely IEL from mice. We report here that by contrast with the DEC gamma delta, the IEL gamma delta TCR are structurally diverse.