Analysis of the genome structure of tobacco rattle virus strain PSG.

The sequence of the 3'-terminal 2077 nucleotides of genomic RNA 1 and the complete sequence of genomic RNA 2 of tobacco rattle virus (TRV, strain PSG) has been deduced. RNA 2 (1905 nucleotides) contains a single open reading frame for the viral coat protein (209 amino acids), flanked by 5'- and 3'-noncoding regions of 570 and 708 nucleotides, respectively. A subgenomic RNA (RNA 4) was found to lack the 5'-terminal 474 nucleotides of RNA 2 and is the putative messenger for coat protein. The deduced RNA 1 sequence contains the 3'-terminal part of a reading frame that probably corresponds to the TRV 170K protein and reading frames for a 29K protein and a 16K protein. Proteins encoded by the first two reading frames show significant amino acid sequence homology with corresponding proteins encoded by tobacco mosaic virus. Subgenomic RNAs 3 (1.6 kb) and 5 (0.7 kb) were identified as the putative messengers for the 29K and 16K proteins, respectively. At their 3'-termini all PSG-RNAs have an identical sequence of 497 nucleotides; at the 5'-termini homology is limited to 5 to 10 bases.     

Correlation between mechanical properties and wall composition of the canine superior vena cava

The mechanical properties (modulus of elasticity and stress-relaxation) of different venous segments of the canine superior vena cava were determined as well as the composition of the vessel wall by means of physical, biochemical and histological methods. It was found that the wall of the vena cava was structurally and mechanically a function of the metric position with respect to the right heart: the modulus of elasticity increased, the stress-relaxation decreased, the concentration of hydroxyproline, collagen and elastin increased and the amount of muscle fibres decreased with increasing distal distance from the right heart. A significant linear correlation coefficient was observed between the modulus of elasticity and the structural wall components. The data presented show the axial heterogeneity and the dependency of the mechanical properties upon the venous vessel wall composition.     

DoesGonyaulax polyedra measure a week?

Cell communication was investigated inGonyaulax polyedra by mixing two cultures grown on opposite lighting regimens, as reported in a companion paper (1). Herein, using the same data, 7-d (circaseptan) rhythms are also shown to characterize the luminescence of this cellular organism. A fraction of a culture ofG. polyedra, grown in 12 h of light (L), alternating with 12 h of darkness (D), was exposed for 3 d to an LD-shift by 11 h. The circadian glow rhythm was compared under free-running conditions (LL) for cultures previously kept on the two differing LD regimens and for mixed cultures. A circaseptan modulation of the circadian amplitude is detected in cultures that had not undergone an LD shift and in some of the mixed cultures, but not in the shifted cultures. A statistically significantly lower circaseptan amplitude (<50%) and acrophase advance of over 120° or 56 h (p<0.001) characterizes the mixed cultures, as compared to the original unshifted cultures, a finding that could mean thatG. polyedra communicates along a circaseptan frequency. Whether a prior phase-shift known to affect circaseptan behavior in another unicell,Acetabularia mediterranea, led to an alteration of the time structure ofG. polyedra remains an interesting subject for further study in this model, a model attractive to students of unicellular rhythms and underlying mechanisms that henceforth should be studied at multiple circadian and circaseptan frequencies. Circadian and circaseptan interrelations can both serve as markers for mechanisms of intercellular communication.     

Ribosomal DNA sequences detected in malaria parasites by cytochemical hybridization

A procedure in which fluorochrome-labelled RNA is hybridized in situ to homologous DNA sequences was used to investigate the possible application of this method to the human malaria parasite Plasmodium falciparum. Rhodamine-labelled ribosomal RNA stained the nuclei of the parasites after cytochemical hybridization. This result demonstrates that ribosomal RNA genes can be visualised. It was estimated that the hybridization efficiency was greater than 40%.     

Regulation of rat ovarian cell growth and steroid secretion

A cultured rat ovarian cell line (31 A-F(2)) was used to study the effect of growth factors (epidermal growth factor [EGF] and fibroblast growth factor [FGF]), a survival factor (ovarian growth factor [OGF]), a hormone (insulin), and an iron-binding protein (transferring) on cell proliferation and steroid production under defined culture conditions. EGF and insulin were shown to be mitogenic (half-maximal response at 0.12 nM and 0.11 muM, respectively) for 31A-F(2) cells incubated in serum-free medium. EGF induced up to three doublings in the cell population, whereas insulin induced an average of one cell population doubling. FGF, OGF, and transferrin were found not to have any prominent effect on cell division when incubated individually with 31A-F(2) cells in serum-free medium. However, a combination of EGF, OGF, insulin, and transferrin stimulated cell division to the same approximate extent as cells incubated in the presence of 5 percent fetal calf serum. EGF or insulin did not significantly affect total cell cholesterol levels (relative to cells incubated in serum-free medium) when incubated individually with 31A-F(2) cells. However, cell cholesterol levels were increased by the addition of OGF (250 percent), FGF (370 percent), or a combination of insulin and EGF (320 percent). Progesterone secretion from 31A-F(2) cells was enhanced by EGF (25 percent), FGF (80 percent), and insulin (115 percent). However, the addition of a mitogenic mixture of EGF, OGF, insulin, and transferrin suppressed progesterone secretion 150 percent) below that of control cultures. These studies have permitted us to determine that EGF and insulin are mitogenic factors that are required for the growth of 31A-F(2) cells and that OGF and transferrin are positive cofactors that enhance growth. Also, additional data suggest that cholesterol and progesterone production in 31A-F(2) cells can be regulated by peptide growth factors and the hormone insulin.     

A transferrin-binding protein of Trypanosoma brucei is encoded by one of the genes in the variant surface glycoprotein gene expression site.

A transferrin-binding protein (TFBP) with an apparent molecular weight of 42 kd was purified from detergent-soluble membrane proteins of bloodstream forms of Trypanosoma brucei. The protein is not expressed in the insect-borne stage of the parasite's life-cycle. Purified TFBP can be converted from an amphiphilic to a hydrophilic form by cleavage with T.brucei glycosylphosphatidylinositol (GPI)-specific phospholipase C, demonstrating that the C-terminus is modified by a GPI-membrane anchor. The TFBP is encoded by an expression-site-associated gene [ESAG 6 in the nomenclature of Pays et al. (1989) Cell, 57, 835-845] which is under the control of the promoter transcribing the expressed variant surface glycoprotein gene. The possible function of TFBP as a receptor for the uptake of transferrin in bloodstream forms is discussed.     

Homology between chitinases that are induced by TMV infection of tobacco

Recently, four chitinases have been detected in tobacco mosaic virus (TMV) infected tobacco: two acidic chitinases that were identified as pathogenesis-related (PR) proteins P and Q and two basic chitinases (Legrand et al., Proc.Natl. Acad. Sci. USA, in press). Here, it was shown that P and Q are closely serologically related but not related to other known acidic tobacco PR proteins. Antisera to P and Q were used to characterize translation products of TMV-induced mRNAs that were hybrid-selected with cDNA clones described previously (Hooft van Huijsduijnen et al., EMBO J 5: 2057–2061, 1986). In this way cDNA clones corresponding to the acidic and basic chitinases were identified. The partial amino acid sequences of the acidic and basic tobacco chitinases that were represented in the clones, showed an approximately 70% homology to each other and to the sequence of a bean chitinase. Although the acidic and basic chitinases differ in apparent molecular weight, they were found to have homologous C-termini.Hybridization of cDNA probes to genomic blots indicated that the acidic and basic chitinases are each encoded by two to four genes in the amphidiploid genome of Samsun NN tobacco. A similar complexity was found for the genes encoding the tobacco PR protein that is homologous to the sweet-tasting protein thaumatin and to the bifunctional trypsin/-amylase inhibitor from maize.