Marker rescue from bleomycin-treated Chlamydomonas reinhardi

A new method has been developed for gene transfer in eukaryotic cells. Chlamydomonas reinhardi, a unicellular eukaryotic alga, was treated with a lethal dose of bleomycin, an agent that induces chromosome breakage. Bleomycin-treated cells were mated with untreated cells, and the mixture was plated onto selective agar medium. The progeny that arose contained the genetic markers from the untreated parent plus a subset of the genetic markers from the bleomycin-treated parent. Those markers derived from the untreated parent were stable, whereas those recovered from the bleomycin-treated parent were often unstable. Markers closely linked in the bleomycin-treated parent were usually rescued or lost together, whereas distantly linked or unlinked markers were rescued or lost independently. These results suggest that bleomycin treatment of C. reinhardi leads to the formation of chromosome fragments, and fusion of bleomycin-treated cells to untreated cells results in the rescue of some of these fragments. This procedure provides a new means of gene transfer that may be useful for genetic mapping, genetic engineering and for the study of genetic organization.