<P> Principal interactions of structural proteins are at cadherin - based adherens junction . Actin filaments are linked to α - actinin and to the membrane through vinculin . The head domain of vinculin associates to E-cadherin via α - catenin, β - catenin, and γ - catenin . The tail domain of vinculin binds to membrane lipids and to actin filaments . </P> <P> Actin has been one of the most highly conserved proteins throughout evolution because it interacts with a large number of other proteins . It has 80.2% sequence conservation at the gene level between Homo sapiens and Saccharomyces cerevisiae (a species of yeast), and 95% conservation of the primary structure of the protein product . </P> <P> Although most yeasts have only a single actin gene, higher eukaryotes, in general, express several isoforms of actin encoded by a family of related genes . Mammals have at least six actin isoforms coded by separate genes, which are divided into three classes (alpha, beta and gamma) according to their isoelectric points . In general, alpha actins are found in muscle (α - skeletal, α - aortic smooth, α - cardiac), whereas beta and gamma isoforms are prominent in non-muscle cells (β - cytoplasmic, γ1 - cytoplasmic, γ2 - enteric smooth). Although the amino acid sequences and in vitro properties of the isoforms are highly similar, these isoforms cannot completely substitute for one another in vivo . </P> <P> The typical actin gene has an approximately 100 - nucleotide 5' UTR, a 1200 - nucleotide translated region, and a 200 - nucleotide 3' UTR . The majority of actin genes are interrupted by introns, with up to six introns in any of 19 well - characterised locations . The high conservation of the family makes actin the favoured model for studies comparing the introns - early and introns - late models of intron evolution . </P>

What is the role of actin in eukaryotic cells