Most types of cells are known from their structure and overall form to
possess a characteristic organization. In some instances this is evident in
the non-random disposition of organelles and such system subunits as
cisternae of the endoplasmic reticulum or the Golgi complex. In others it
appears in the distribution and orientation of cytoplasmic fibrils. And in
yet others the organization finds expression in the non-random distribution
and orientation of microtubules, especially as found in highly anisometric
cells and cell processes. The impression is unavoidable that in none of
these cases is the organization achieved without the involvement of the
cytoplasmic ground substance (CGS) or matrix. This impression is based on
the fact that a matrix is present and that in all instances these formed
structures, whether membranelimited or filamentous, are suspended in it. In
some well-known instances, as in arrays of microtubules which make up
axonemes and axostyles, the matrix resolves itself into bridges (and spokes)
between the microtubules, bridges which are in some cases very regularly
disposed and uniform in size (Mcintosh, 1973; Bloodgood and Miller, 1974;
Warner and Satir, 1974).
A Vacuolar Sorting Domain May Also Influence the Way in Which Proteins Leave the Endoplasmic Reticulum