One gap junction consists of a cluster of closely packed pairs of transmembrane channels, the connexons, through which materials of low MW diffuse from one cell to a neighboring cell. A connexon is composed of a hexamer of connexins. Expressed in ovarian somatic cells, heart, leg muscle, liver and eye but not in brain. Maternal protein whose levels decrease in late stages of oocyte maturation. Belongs to the connexin family. Alpha-type (group II) subfamily.