48‐kilodalton intermediate‐filament‐associated protein in astrocytes

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Abstract
We provide evidence that a protein of 48 kilodaltons (KD), recognized by a normal rebbit serum (F2N), is associated with intermediate filaments (IF) of astrocytes both in cell cultures and in situ. Immunofluorescence staining shows that the F2N serum gives a fibrous staining pattern similar to that seen with antiserum to glial filament protein (GFP), a protein sepecific for IF of astrocytes, and that both proteins are present in the perinuclear fibrous aggregates of IF produced by treating the cells with colchicine. At the ultrastructural level the gold particles decorating the 48‐KD protein are localized on the IF in a linear patterns. This difference in distribution and the fact that the two proteins have different electrophoretic mobilities on SDS gels indicates that the 48‐KD protein although associated with IF is different from GFP. The 48‐KD protein appears to be a distinct, developmentally regulated intermediate‐filament‐associated protein (IFAP), different from other IFAP'S reported to date and the first IFAP described in astrocytes. Its appearance in late developmental stages when motile astroblasts are changing into nonmotile setllate cells suggests that the 48‐KD protein may be involved in cross‐linking the GFP‐containing IF to provide more tensile stregth to the cytoplasm at the expense of flexibility.

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