Three macronuclear molecules encoding three highly divergent actin genes in Oxytricha nova

Abstract

A third macronuclear actin gene, designated as actin III, of the ciliated protozoan Oxytricha nova was isolated from a small library of macronuclear DNA molecules cloned in plasmid PUC19. This molecule encodes a putative protein of 374 amino acids. The actin I and actin III genes are identical in 61% of amino acid positions, and the actin II and actin III genes are 50% identical. All three actin proteins have only 49% to 68% amino acid identities with actins in other eukaryotes. Thus, the three actin genes in O. nova represent extreme divergence both among themselves and from actin genes in other eukaryotes, including two other ciliates.