The relationship between the fatty acid profiles of the yolk and the embryonic tissue lipids: A comparison between the lesser black backed gull (Larus fuscus) and the pheasant (Phasianus colchicus)

Although substantial information is available regarding the fatty acid composition of lipids of the yolk and of the developing tissues of the chicken embryo, there is little knowledge on this topic for other avian species. The aim of the present study was to compare the yolk and embryonic tissue fatty acid profiles for a species selecting its food in the wild (the lesser black backed gull) with one fed on a standard commercial diet (the commercially reared pheasant). The fatty acid compositions of the yolk lipids were determined, and major differences were observed between the two species. In particular, the phospholipid of the gull yolk was enriched in 20:4n-6 and 22:6n-3 (18.8 and 7.1%, respectively, by weight of total fatty acids) in comparison with the pheasant (4.0 and 4.1%, respectively). The fatty acid compositions of the embryonic tissues were determined using eggs incubated in the laboratory. For the liver and heart, the fatty acid composition of the lipids in the two species reflected the initial yolk composition, with the gull tissue lipids generally containing higher proportions of 20:4n-6 and 22:6n-3 than those of the pheasant. In contrast, the fatty acid profiles of the brain phospholipid were essentially identical in the two species, with 20:4n-6 and 22:6n-3 comprising approximately 9 and 17%, respectively, of total fatty acids in both cases.     

Core protein mu2 is a second determinant of nucleoside triphosphatase activities by reovirus cores.

NTPase activities in mammalian reovirus cores were examined under various conditions that permitted several new differences to be identified between strains type 1 Lang (T1L) and type 3 Dearing (T3D). One difference concerned the ratio (at pH 8.5) of ATP hydrolysis at 50 degrees C to that at 35 degrees C. A genetic analysis using T1L x T3D reassortant viruses implicated the L3 and M1 gene segments in this difference, with M1 influencing ATPase activity most strongly at high temperatures. L3 and M1 encode the core proteins lambda1 and mu2, respectively. Another difference concerned the absolute levels of GTP hydrolysis by cores at 45 degrees C and pH 6.5. A genetic analysis using T1L x T3D reassortants implicated the M1 gene as the sole determinant of this difference. The results of these experiments, coupled with previous findings (S. Noble and M. L. Nibert, J. Virol. 71:2182-2191, 1997), suggest either that a single type of NTPase in cores is strongly influenced by two different core proteins--lambda1 and mu2--or that cores contain two different types of NTPase influenced by the two proteins. The findings appear relevant for understanding the complex functions of reovirus cores in RNA synthesis and capping.     

Escherichia coli heat-labile enterotoxin. Nucleotide sequence of the A subunit gene

We report the complete DNA sequence of the Escherichia coli elt A gene, which codes for the A subunit of the heat-labile enterotoxin, LT. The amino acid sequence of the LT A subunit has been deduced from the DNA sequence of elt A. The LT A subunit starts with methionine, ends with leucine, and comprises 254 amino acids. The computed molecular weight of LT A is 29,673. The A subunit of cholera toxin (CT A) has been shown to be structurally and functionally related to the LT A subunit. Comparison of the primary structure of LT A with the known partial amino acid sequence of CT A indicates that the 2 polypeptides share considerable homology throughout their sequences. The NH2-terminal regions exhibit the highest degree of homology (91%), while the COOH-terminal region, containing the sole cystine residue in each toxin is less conserved (approximately 52%). Alignment of homologous residues in the COOH-terminal regions of LT A and CT A indicates that a likely site for proteolytic cleavage of LT A is after Arg residue 188. The resulting A2 polypeptide would be 46 amino acids long, would contain a single cysteine residue, and have Mr = 5261. The elt A nucleotide sequence further predicts that the LT A protein is synthesized in a precursor form, possessing an 18-amino acid signal sequence at its NH2 terminus.     

Effects of exogenous wild-type p53 on a human lung carcinoma cell line with endogenous wild-type p53

Several studies have shown that expression of exogenous wild-type p53 is detrimental to the growth of cell lines with absent or mutant p53. In this study, wild-type p53 cDNA expression plasmids were transfected into A549 lung carcinoma cells which had previously been shown by sequencing to contain wild-type p53. When a constitutively expressed wild-type p53 plasmid containing the neomycin resistance gene was transfected into these cells, no G418-resistant colonies contained the exogenous p53 cDNA even though the neomycin resistance gene was integrated. When cells were transfected with a dexamethasone-inducible wild-type p53 cDNA expression plasmid, induction of p53 expression resulted in a decreased growth rate and a decreased proportion of S-phase cells. Continuous treatment with dexamethasone resulted in continued p53 expression for 16 days, but beyond that time expression ceased and could not be reinduced. These data indicated that although the A549 cell line could proliferate in the presence of endogenous wild-type p53 there was a strong selection pressure against continued expression of additional exogenous wild-type p53.     

Comparison of the refined crystal structures of liganded and unliganded chicken, yeast and trypanosomal triosephosphate isomerase.

The refined crystal structures of chicken, yeast and trypanosomal triosephosphate isomerase (TIM) have been compared. TIM is known to exist in an "open" (unliganded) and "closed" (liganded) conformation. For chicken TIM only the refined open structure is available, whereas for yeast TIM and trypanosomal TIM refined structures of both the open and the closed structure have been used for this study. Comparison of these structures shows that the open structures of chicken TIM, yeast TIM and trypanosomal TIM are essentially identical. Also it is shown that the closed structures of yeast TIM and trypanosomal TIM are essentially identical. The conformational difference between the open and closed structures concerns a major shift (7 A) in loop-6. Minor shifts are observed in the two adjacent loops, loop-5 (1 A) and loop-7 (1 A). The pairwise comparison of the three different TIM barrels shows that the 105C alpha atoms of the core superimpose within 0.9 A. The sequences of these three TIMs have a pairwise sequence identity of approximately 50%. The residues that line the active site are 100% conserved. The residues interacting with each other across the dimer interface show extensive variability, but the direct hydrogen bonds between the two subunits are well conserved. The orientation of the two monomers with respect to each other is almost identical in the three different TIM structures. There are 56 (22%) conserved residues out of approximately 250 residues in 13 sequences. The functions of most of these conserved residues can be understood from the available open and closed structures of the three different TIMs. Some of these residues are quite far from the active site. For example, at a distance of 19 A from the active site there is a conserved saltbridge interaction between residues at the C-terminal ends of alpha-helix-6 and alpha-helix-7. This anchoring contrasts with the large conformational flexibility of loop-6 and loop-7 near the N termini of these helices. The flexibility of loop-6 is facilitated by a conserved large empty cavity near the N terminus of alpha-helix-6, which exists only in the open conformation.     

Specific Expression of N-Acetylaspartate in Neurons, Oligodendrocyte-Type-2 Astrocyte Progenitors, and Immature Oligodendrocytes In Vitro

To test the specificity of N-acetylaspartate (NAA) as a neuronal marker for proton nuclear magnetic resonance (1H NMR) spectroscopy, purified and characterized cultured cells were analyzed for their NAA content using both 1H NMR and HPLC. Cell types studied included cerebellar granule neurons, type-1 astrocytes, meningeal cells, oligodendrocyte-type-2 astrocyte (O-2A) progenitor cells, and oligodendrocytes. A high concentration of NAA was found in extracts of cerebellar granule neurons (approximately 12 nmol/mg of protein), whereas NAA remained undetectable in purified type-1 astrocytes, meningeal cells, and mature oligodendrocytes. However, twice the neuronal level of NAA was found in O-2A progenitors grown in vitro. In addition significant levels of NAA were also detected in cultures of immature oligodendrocytes. Our data partly support previous suggestions that NAA may be a useful neuronal marker for 1H NMR spectroscopic examination of the adult brain. However, they also raise the further possibility that alterations of NAA associated with some specific brain disorders, particularly disorders seen in newborn and young children, may reflect abnormalities in the development of oligodendroglia or their precursors.