Rat liver gap junction protein: properties and partial sequence.

Gap junctions, strongly implicated as channels for direct cell-to-cell communication, have been isolated from rat liver in high yield and purity. These gap junction fractions contain few morphologically recognizable contaminants, but NaDodSO4/polyacrylamide gel electrophoresis reveals a number of polypeptides. With the exception of a nonjunctional component of Mr 38,000 and some poorly soluble material, including collagen, all the polypeptides have very similar or identical two-dimensional peptide maps and arise from proteolytic cleavage of the COOH-terminus or aggregation of a Mr 28,000 protein. We report the sequence of the NH2-terminal 52 amino acids of this protein. The polypeptide (Mr approximately equal to 10,000) characteristic of trypsin-treated gap junction preparations is shown to be two distinct polypeptides, both derived from the Mr 28,000 protein.