Isolation and characterization of polyoma nucleoprotein complexes.
A method for the isolation of polyoma nucleoprotein complexes has been developedusing neuraminidase treatment of infected cell lysates. At least three distinct forms of polyoma virion intermediates were identified by their [3H]thymidine labeling kinetics and sedimentation coefficients: a rapidly labeled 95 S "replicating complex" which chases to a 75 S minichromosome and then to a 240 S virion structure. The general properties of these distinct intermediates were similar to those found for SV40. In contrast to SV40, however, a continuum of labeled polyoma viral DNA sedimented between 240 S and 95 S. These complexes were characterized by their release from cell debris with neuraminidase, precipitation with antivirion antibody, complete disruption in 1 M NaCl, and association with hemagglutinating (HA) activity. These intermediates may represent incremental capsid protein additions to the 75 S minichromosome, hypothesized in the currentmodels for SV40 assembly. The ability to isolate a complete complement of polyoma subviral complexes provides a basis for studying the growth defect of polyoma host-range mutants, and the properties of neuraminidase release, hemagglutination, and specific immunoprecipitation suggest purification steps for further characterization of these virion assembly intermediates.