[Analysis of a chromosomal DNA fragment isolated from a hybrid autonomous plasmid of Chlamydomonas reinhardtii].

The ability of a previously cloned fragment of nuclear DNA of Chlamydomonas reinhardtii (a 2.4-kb BamH 1-EcoR I fragment) to function as the origin of replication of plasmid pARG7.8.2.4, carrying the homologous arg7 marker gene of prototrophy or arginine in cells of C. reinhardtii transformants, was studied. As shown by Southern blotting, plasmid pARG7.8.2.4 integrates at several sites of chromosomal DNA of chlamydomonas without autonomous maintenance in cells. Results obtained using Southern blotting and plasmid rescue techniques demonstrated that plasmid pARG7.8, containing only the arg7 gene, is able both to integrate into the chromosome and to be maintained, in some cases, in the autonomous state in Arg+ transformants of alga. Analysis of the nucleotide sequence of the DNA fragment under study revealed several types of GC-enriched repeats that manifested homology with the nucleotide sequence of the arg7 gene in introns 10 and 12.