The nucleosome structure of the rRNA genes of some tumorous and nontumorous Nicotiana cell lines.

The nucleosome structure of the nuclear rRNA genes was investigated in a variety of tumorous and nontumorous Nicotiana tabacum cell lines, and in a genetic tumor produced by crossing Nicotiana langsdorffii with Nicotiana glauca. The rRNA genes from two unorganized octopine type crown gall tumors were found in an altered nucleosome conformation compared to those of the other cell lines and N. tabacum leaves. The altered nucleosome structure of the rRNA genes in the octopine type crown gall lines was not due to the tumorous state of the tissue, nor was it related directly to the morphology of the tumor. These two lines did have, however, a greatly reduced rRNA gene copy number. Several Eco R1 fragments homologous to the rRNA gene probe were preferentially lost from one of these tumor lines. The alteration of the nucleosome structure of the remaining rRNA genes in the octopine type crown gall tumors may result from rapid transcription necessitated by their reduced copy number.