Reassembled HVJ (Sendai virus) envelopes containing non-toxic mutant proteins of diphtheria toxin show toxicity to mouse L cell

Abstract

PREVIOUS studies from this laboratory have described the preparation, from HVJ virions solubilised with a non-ionic detergent, of a reassembled envelope fraction free of nucleocapsids. Such reconstituted envelopes still retain neuraminidase, haemagglutinating, cell fusion and haemolytic activities^1–3. Since intact virions release their nucleoproteins into the cytoplasm after fusion with mammalian cells, it seemed possible that any given macromolecule contained within such a reassembled viral envelope might be introduced into susceptible mammalian cells by this means. We report here the successful application of this method to the introduction of CRM45, a non-toxic mutant protein related to diphtheria toxin⁴, into mouse L cells, a strain that is normally toxin resistant. Although CRM45 is a potent NAD : elongation factor 2-ADP ribosyl (NAD : EF2-ADPR) transferase^5,6 and thus blocks protein synthesis in eukaryotic cell extracts, it is non-toxic for animal cells because it lacks a C-terminal sequence of amino acids necessary to bind to susceptible cell membranes and thus cannot reach the cell interior⁷. If a few molecules of CRM45 could be introduced into the living cell cytoplasm, they should block protein synthesis and kill the cells. This has now been accomplished by fusion of CRM45-containing reassembled HVJ envelopes with cultured mouse L cells.