CHLOROPLAST DNA EVIDENCE FOR THE INTERRELATIONSHIPS OF TOMATOES,POTATOES, AND PEPINOS (SOLANACEAE)

We used chloroplast DNA restriction site analysis to test hypotheses of relationships of Solarium subgenus Potatoe (including potatoes and pepinos), two other Solanum, Cyphomandra (the tree tomatoes), and Lycopersicon (the tomatoes). Capsicum and Datura were used as outgroups. The results support two main clades among the taxa we studied: 1) Solanum subgenus Potatoe and Lycopersicon; and 2) other Solanum and Cyphomandra. Within the first clade, the following groups were supported: a) sect. Basarthrum and sect. Anarrhichomenum; b) sect. Etuberosum; c) sect. Petota; d) sect. Juglandifolium, including subsect. Lycopersicoides; and e) the genus Lycopersicon. These results, in combination with an analysis of morphological data, advocate the controversial, but previously suggested, treatment of Lycopersicon as congeneric with Solanum in subgenus Potatoe. Thus, the cultivated tomato will be recognized as Solanum lycopersicum L. Solanum chmielewskii and Solanum lycopersicum var. cerasiforme are proposed as new combinations; Solanum neorickii is proposed as a new name for Lycopersicon parviflorum. Our data also suggest that Cyphomandra should be included within Solanum.     

A new ATP-binding fold in actin, hexokinase and Hsc70

One of a cell biologist's favourite occupations is to discover the proteins that perform newly described functions in the cell. Very often lately, this has resulted in the identification of protein families whose related amino acid sequences reflect similar functions, but can proteins with totally unrelated sequences have similar structures and functions? In this review, Ken Holmes, Chris Sander and Alfonso Valencia describe the structural similarities between three well-known proteins that have no readily detectable primary sequence similarities but for which X-ray crystallography has revealed very similar structures. A comparison of their structures provides insights into their common mechanisms of action and into protein evolution, and has been used to detect related proteins in sequence data bases.     

Evidence for a functional role of RNA in centrioles.

Basal bodies, purified from Chlamydomonas and Tetrahymena, were exposed to various enzymatic treatments and then assayed for their ability to nucleate aster formation upon injection into eggs of Xenopus laevis. Untreated basal bodies injected into frog eggs act as centrioles and induce the formation of asters. The aster-inducing activity of basal bodies was eliminated by treatment with proteolytic enzymes and ribonucleases. Aster-inducing activity was not affected by DNAse and a number of other enzymes. The effect of proteolytic digestion on aster-inducing activity appeared to be directly correlated with the degree of structural damage to the basal body. Low concentrations of pancreatic ribonuclease A, ribonuclease T1, and S1 nuclease also completely abolished aster-inducing activity, although these enzymes had no effect on basal body structure. Ribonuclease-treated basal bodies remained capable of supporting microtubule elongation in vitro. Preliminary evidence indicates that basal bodies from Chlamydomonas and Tetrahymena contain about 5 x 10(-16) g of RNA which co-band with basal bodies and aster-inducing activity by equilibrium density gradient sedimentation. We conclude first, that centrioles contain RNA which is required for initiation of aster formation, and second, that the centriole activity or ability to assemble a mitotic aster is separable from the basal body activity, or ability to serve directly as a template for microtubule growth.     

Mild dehydration and atrial natriuretic peptide in young and elderly subjects.

The influence of mild dehydration on plasma levels of atrial natriuretic peptide (ANP) was studied in both young (aged 18 to 25 years) and elderly (aged 72 to 86 years) subjects. We expected that dehydration would lower ANP concentrations due to the ensuing volume contraction. A different response of the ANP hormonal system in the elderly might help to explain the observation that elderly subjects are more predisposed to dehydration as compared to young subjects. Dehydration was induced by restriction of fluid intake to 25% of normal for one day. During the study, urinary osmolality increased while osmolar clearance and body weight decreased. Basal ANP concentrations were higher in the elderly subjects. However, these levels did not change during the dehydration study neither in the young nor in the elderly subjects. This may be explained by the activation of counter-regulatory systems preventing a decrease in central blood volume and hence a decrease in ANP concentration.     

Enzymological characterization of a putative canine analogue of primary hyperoxaluria type 1.

This paper concerns an enzymological investigation into a putative canine analogue of the human autosomal recessive disease primary hyperoxaluria type 1 (alanine:glyoxylate/serine:pyruvate aminotransferase deficiency). The liver and kidney activities of alanine:glyoxylate aminotransferase and serine:pyruvate aminotransferase in two Tibetan Spaniel pups with familial oxalate nephropathy were markedly reduced when compared with a variety of controls. There were no obvious deficiencies in a number of other enzymes including D-glycerate dehydrogenase/glyoxylate reductase which have been shown previously to be deficient in primary hyperoxaluria type 2. Immunoblotting of liver and kidney homogenates from oxalotic dogs also demonstrated a severe deficiency of immunoreactive alanine:glyoxylate aminotransferase. The developmental expression of alanine:glyoxylate/serine:pyruvate aminotransferase was studied in the livers and kidneys of control dogs. In the liver, enzyme activity and immunoreactive protein were virtually undetectable at 1 day old, but then increased to reach a plateau between 4 and 12 weeks. During this period the activity was similar to that found in normal human liver. The enzyme activities and the levels of immunoreactive protein in the kidneys were more erratic, but they appeared to increase up to 8 weeks and then decrease, so that by 36 weeks the levels were similar to those found at 1 day. The data presented in this paper suggest that these oxalotic dogs have a genetic condition that is analogous, at least enzymologically, to the human disease primary hyperoxaluria type 1.