Studies of chloroplast development in Euglena: XII. Two types of satellite DNA

Abstract

Three species of DNA from wild-type cells of Euglena gracilis var. bacillaris are described. Main band DNA (density = 1·707 g/cm3) most probably is assignable to the nucleus and is found in all strains examined. The satellite region (density = 1·688 g/cm3) previously described ( Leff, Mandel, Epstein & Schiff, 1963 ) has now been resolved into two DNA satellites, Sc (density = 1·686 g/cm3) and Sx (density = 1·691 g/cm3), both of which are present in wild-type cells, Sc is found in enriched quantities in the chloroplast fraction of green cells and is found in light-grown and dark-grown wild-type cells and in all mutants capable of forming at least a partial chloroplast, but is absent from all mutants incapable of plastid formation. Conversion of strains capable of chloroplast formation to strains incapable of this by means of ultraviolet treatment brings about a loss of Sc. This is consistent with ScDNA being a constituent of the chloroplasts. Sx is found in wild-type cells and in all mutants examined, whether capable or incapable of forming chloroplasts. On cell fractionation, Sx is absent from the chloroplast fraction and is found in the small-particle fraction of the cells along with mitochondrial cytochromes. From density calculations, main band DNA contains 48% guanine+cytosine : 52% adenine+thymine; Sx contains 31% guanine+cytosine: 69% adenine+thymine; and Sc contains 26% guanine+cytosine : 74% adenine+thymine. All three DNA species appear to be double-stranded.