Quantitative investigation of murine cytomegalovirus nucleocapsid interaction

In this study, we quantitatively investigate the role of the M97 protein for viral morphogenesis in murine cytomegalovirus (MCMV)-infected fibroblast cells. For this purpose, a statistical analysis is performed for the spatial distribution of nuclear B-capsids (devoid of DNA, containing the scaffold) and C-capsids (filled with DNA). Cell nuclei infected with either wild-type or an M97 deletion mutant were compared. Univariate and multivariate point process characteristics (like Ripley's K-function, the L-function and the nearest neighbour distance distribution function) are investigated in order to describe and quantify the effects that the deletion of M97 causes to the process of DNA packaging into nucleocapsids. The estimation of the function L(r) -r reveals that with respect to the wild type there is an increased frequency of point pairs at a very short distance (less than approximately 100 nm) for both the B-capsids as well as for the C-capsids. For the M97 deletion mutant type this is no longer true. Here only the C-capsids show such a clustering behaviour, whereas for B-capsids it is almost nonexistant. Estimations of functionals such as the nearest neighbour distance distribution function confirmed these results. Thereby, a quantification is provided for the effect that the deletion of M97 leads to a loss of typical nucleocapsid clustering in MCMV-infected nuclei.