Inhibition of nuclear export of ribonucleoprotein complexes of influenza virus by leptomycin B

We have studied nuclear export of influenza virus components using an in vitro transport system with digitonin-treated infected cells. We first monitored the efficiency of export of the viral ribonucleoprotein (vRNP) complex by analyzing viral components with western blotting. We used leptomycin B (LMB), an inhibitor of nuclear export signal (NES)-and its receptor, CRM1/Exportin1-mediated protein export. LMB efficiently inhibited vRNP export, while it did not affect the subcellular localization and export of matrix protein (M) 1 and nonstructural protein (NS) 2. Second, indirect immunofluorescence assays also revealed that vRNP export is sensitive to LMB. NS2 in NS2-transfected cells was not accumulated in nuclei in the presence of LMB, while NS2 in infected cells was found slightly accumulated in nuclei in the presence of LMB. Finally, we performed in vitro RNA synthesis assays using digitonin-treated infected cells and exported fractions. The exported vRNP was RNA synthesis-competent. Analyses using glycerol density gradients showed that a major fraction of M1 and NS2 was not complexed with the exported vRNP. These results suggest that nuclear export of RNA synthesis-competent vRNP is dependent on a LMB-sensitive pathway and that there would be two types of NS2, i.e. LMB-sensitive and -insensitive NS2. The involvement of viral late proteins in vRNP export during late stages of infection is discussed.

Mapping of functional sites on the primary structure of the tail lysozyme of bacteriophage T4 by mutational analysis

Tail lysozyme of bacteriophage T4, product of gene 5 (gp5), functions upon infection by locally digging a hole in the peptidoglycan layer, so that the tail tube, through which the phage DNA is injected, can penetrate to the inner membrane. It has been inferred from DNA sequence and expression of the tail lysozyme on a plasmid in Escherichia coli that the tail lysozyme is synthesized as a precursor of 62 K and is later cleaved to form a mature tail lysozyme of 42 K. Furthermore, gp5 has a region that is highly homologous to T4 lysozyme, gpe, that is the product of gene e and functions for 'lysis from within'. As an approach to elucidation of structure-function relationship of gp5, we determined mutational sites of gene 5 mutants that have heat sensitive virions, are temperature sensitive for growth, or require an amber suppressor. All the mutational sites were mapped in the region corresponding to the mature tail lysozyme. Among the ts mutants, 5ts1 was a pseudo-revertant of an amber mutant which bypasses gene e. It was mapped in the region which had a high homology to gpe, which is well known as T4 lysozyme. The other mutational sites will be also discussed in relation to the phenotypes of the mutants.

Role of O-linked carbohydrate of human urinary trypsin inhibitor on its lysosomal membrane-stabilizing property

Human urinary trypsin inhibitor (UTI) was digested with various enzymes to obtain O-glycoside linked N-terminal glycopeptide (UTIm1), N-glycoside linked C-terminal tandem Kunitz-domains (domain I and II, UTIm2), UTI lacking O-glycoside (UTIc), asialo UTI (UTIa) and UTI lacking N-glycoside (UTIn). We investigated the membrane stabilizing effect of these UTI derivatives on rat renal lysosome by measurement of lysosomal enzyme N-acetyl-beta-D-glucosaminidase (NAG) release after hypotonic treatment. Intact UTI suppressed NAG release, but aprotinin, gabexate mesilate (FOY), nafamostat mesilate (FUT) and recombinant domain II of UTI (R-020) had no effect, indicating that inhibition of serine proteases was not involved and the carbohydrate moiety of UTI might be necessary for this property. Among UTI derivatives, UTIm1, UTIm2, UTIm1+ UTIm2, and UTIc had no effect. In contrast, UTIa or UTIn suppressed NAG release. From these results, we conclude that O-glycoside linked core protein without N-glycoside is essential to the lysosomal membrane-stabilizing property of UTI.