Large arrays of tandemly repeated DNA sequences in the green alga Chlamydomonas reinhardtii

We describe the characterization of tandemly repeated DNA sequences, which resemble the satellite DNA sequences of multicellular eucaryotes, in the unicellular green alga Chlamydomonas reinhardtii. Restriction enzymes that cleave C. reinhardtii DNA relatively frequently produce a number of high molecular weight DNA fragments in addition to the bulk of low molecular weight DNA fragments. pTANC 1.5 contains a 1.5 kb Sau3A fragment cloned from one of these large bands. pTANC 1.5 hybridized to at least three large arrays (200 to 700 kb) of tandemly repeated DNA sequences in the cell-wall-deficient strain cw1.5. These arrays are composed of repeat units that are each cleaved once by BamHl into bands of 1.5, 1.9, 2.0 and 2.5 kb in size. The copy numbers of the 1.5, 1.9, 2.0 and 2.5 kb Bamhl bands vary between different C. reinhardtii strains. Chlamydomonas smithii and a number of C. reinhardtii strains are deficient in all four BamHl bands. Genetic analysis of wild-type strain 137c, which is deficient in the 2.0 kb BamHl band, indicates that the 1.5, 1.9 and 2.5 kb BamHl bands derive from at least five loci. The 1.5, 1.9 and 2.5 kb repeat units are not extensively interspersed with each other in strain 137c. Pulsed-field gel electrophoresis of intact C. reinhardtii chromosomes indicates that TANC arrays are present on more than one chromosome.