Abstract

Nucleoli of tissue culture cells were segregated into their fibrillar and granular components by treatment with actinomycin D. Following this segregation, the cells were treated with quinacrine hydrochloride, an agent which selectively sensitizes the nucleoli to argon laser light. The actinomycin D-segregated, quinacrine-sensitized nucleolar components were selectively irradiated with the laser microbeam and subsequent uridine uptake assayed. The data indicate that selective damage to the light area is generally more damaging than damage to the dark area. These results support the idea that DNA is closely associated with the nucleolar fibrillar component. © 1974.