Fine structure of active ribosomal genes.

The structure of active ribosomal genes in the newt Notophthalmus viridescens has been studied at the higher resolution permitted by negative staining. Spherical particles, 70 A to 100 A in diameter are seen on the non-transcribing "spacer" regions, but were absent from certain regions of the transcribing "matrix". The matrix core often appears thicker than a double strand of DNA. These results are discussed in the light of the recently discovered subunit structure of chromatin, and in relation to the question of the disposition of histones during transcription.