In vitro synthesis of the major lens membrane protein.

Abstract

The biosynthetic activity of a polyribosomal fraction isolated from the lens fiber plasma membrane-cytoskeleton complex by DNase I treatment has been assayed. After translation of these pol ribosomes in a reticulocyte cellfree system and analysis of the products by electrophoresis in sodium dodecyl sulfate gels, tfe preferential synthesis of a protein with an apparent molecular weight of 26,000 was observed. By means of immunochemical characterization we showed that this protein, which seems not to be synthesized by "free" polyribosomes, is identical with the major intrinsic plasma membrane protein MP26 of lens fibers. Upon storage, the molecular weight of the newly synthesized protein decreases to about 22,000, a phenomenon that has previously been observed for MP26 in isolated plasma membranes and that may be caused by the presence of a specific proteolytic cleaving site in the protein.

Avian lens spectrin: subunit composition compared with erythrocyte and brain spectrin.

“…In lens fiber cells, actin filaments have been shown by a number of criteria to be closely associated with the plasma membrane (1,33,35,36). The disruption of the actin filament system inhibits lens differentiation in vitro as shown by the cessation of cellular elongation (28).…”

“…Two-dimensional peptide mapping reveals that whereas a-spectrins from chicken erythrocytes, brain, and lens are highly homologous, the 3"-spectrins, although related, have some cell-type-specific peptides and are substantially different from erythrocyte 1% spectrin. Thus, the expression of cell-type-specific 3'-and /3-spectrins may be the basis for the assembly of a spectrin-plasma membrane complex whose molecular composition is tailored to the functional requirements of the particular cell-type.The cytoskeleton of vertebrate lens cells is composed of microtubules, actin filaments, and vimentin-type intermediate filaments (5,20, 21,33,34,36). Recent studies have indicated that the lens cytoskeleton may play an important role in lens differentiation.…”

“…Although the basis of cellular elongation is not fully understood, it has been suggested that it may involve, at least in part, the interaction between actin filaments and the plasma membrane (34,40). In lens fiber cells, actin filaments have been observed frequently in the subcortical region where they appear to be attached to the plasma membrane (1,33,35,36).We have begun to investigate the polypeptide composition of lens cell plasma membranes in order to identify polypeptides involved in this interaction. Initial studies from this laboratory have shown that a polypeptide serologically related to the a-subunit of erythrocyte spectrin is expressed in lens cells and is localized at the cytoplasmic surface of the plasma membrane (37; see also reference 24).…”

“…The cytoskeleton of vertebrate lens cells is composed of microtubules, actin filaments, and vimentin-type intermediate filaments (5,20, 21,33,34,36). Recent studies have indicated that the lens cytoskeleton may play an important role in lens differentiation.…”

“…Although the basis of cellular elongation is not fully understood, it has been suggested that it may involve, at least in part, the interaction between actin filaments and the plasma membrane (34,40). In lens fiber cells, actin filaments have been observed frequently in the subcortical region where they appear to be attached to the plasma membrane (1,33,35,36).…”