Heterogeneity

Heterogeneity

Heterogeneity - More than one kind of virus particle may be involved in virus infection. Heterogeneity may be due to

(i) differences in the lengths of virus particles, e. g. tobravirus and alfalfa mosaic virus

(ii) differences in sedimentation rates, with the size remaining constant, e.g. comoviruses,

(iii) differences in nucleic acid content, again with the size remaining constant, e. g. nepoviruses and

(iv) electrophoretic heterogeneity, which is a reflection in the differences in coat proteins or in assembly.

Viruses with heterogeneous particle populations have been termed 'multicomponent', 'multiparticulate' or divided genome viruses.

The particles are often called top (T), middle (M) and bottom (B), with reference to their position in the density gradient column after centrifugation. When two nucleoprotein particles exist for a virus, they are often designated as middle and bottom particles. It is assumed that the top particle, which often contains no nucleic acid, is lacking.

In the tobraviruses the functional particles are designated as long (L) and short (S) particles, corresponding to the bottom and middle particles, respectively.

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