The genome of Moloney murine leukemia virus(MoMuLV) is composed of two identical RNA molecules joined at their 5’ ends by the dimer linkage structure (DLS). Recently it was shown that in vitro generated MuLV RNa formed dimeric molecules and that dimerization sequences are located within the Psi encapsidation domain between positions 215 and 420. Conditions for the spontaneous dimerization of MuLV RNA fragment encompassing the Psi domain have been investigated. The rate of spontaneous MuLV RNA dimer formation is dependent upon RNA, NaCl and MgCl2 concentrations as well as temperature. Thermal denaturation of in vitro generated dimer RNA of 350 nt, from positions 215 to 565, gave a Tm of about 58-degrees-C in 100 mM NaCl. This Tm value is very close to that found for RNA corresponding to the 5" 755 nt and to the genomic 70 S RNA isolated from virions. According to thermodynamic parameters derived from denaturation curves of MuLV dimer RNA generated in vitro, the dimer linkage structure probably involves short sequences.
The synthesis of a new benzoxazinone derivative suitable to detect early infection of cultured cells with mycoplasmas is described. p-[ß-(7-dimethylamino 1,4-benzoxazin 2-one 3yl)-vinyl]-phenylpropenoic acid was coupled to kanamycin A, an aminoglycoside leading to a cationic fluorescent probe which fluoresces at 600 nm upon excitation at 490 nm. This fluorescent probe is shown to heavily label the glycocallix of all the mycoplasma strains tested which are found to be associated with contaminated cultured cells and to allow an easy and rapid detection of contamination by fluorescence microscopy and flow cytometry.
This paper presents the characterization of a sugar-specific receptor on the surface of human circulating polymorphonuclear cells. With the help of fluorescent neoglycoproteins and flow cytometry, a receptor was identified as being specific for .a.-L-rhamnosyl residues. The number of receptors was 55 000/cell and their affinity reached 2 .times. 108 1 mol-1. This number changes as a function of the biological state of the cells. Indeed, receptor expression was modulated by the presence of other cells. T cells and B cells increased the number of receptors on the granulocyte surface. Expression of the .a.-L-rhamnose-specific lectin was dependent on lymphocyte derived soluble factor(s), which induce(s) growth and differentiation of polymorphonuclear phagocytes. Granulocyte/macrophage colony-stimulating factor (GM-CSF) specifically produced a significant increase in the number of receptors for .a.-L-rhamnose (2-10-fold/cell). This modulation was independent of protein kinase C activators such as phorbol ester, which produced no effect on .a.-L-rhamnose receptor expression. These findings demonstrate that GM-CSF may stimulate post differentiation functions and properties of mature granulocytes.