NUCLEAR TRANSFORMATION OF VOLVOX-CARTERI

Stable nuclear transformation of Volvox carteri was achieved using the cloned V. carteri nitA(+) gene (which encodes nitrate reductase) to c omplement a nitA(-) mutation. Following bombardment of mutant cells wi th plasmid-coated gold particles, putative transformants able to utili ze nitrate as a nitrogen source were recovered with an efficiency of a pproximate to 2.5 x 10(-5). DNA analysis indicated that the plasmid in tegrated into the genome, often in multiple copies, at sites other tha n the nitA locus. Cotransformants were recovered with a frequency of 4 0-80% when cells were cobombarded with a selected and an unselected ma rker. Thus, V. carteri becomes one of the simplest multicellular organ isms that is accessible to detailed molecular studies of genes regulat ing cellular differentiation and morphogenesis.