RNA transcription on the giant lateral loops of the lampbrush chromosomes of the American newt Notophthalmus viridescens.

By counting silver grains in autoradiographs of lampbush chromosomes the rates of incorporation of [3H]adenine, [3H]cytidine, [3H]guanosine and [3H]uridine, administered separately, into RNA on the giant loops of chromosome II of Notophthalmus viridescens, were compared with the rates of incorporation of these same precursors into RNA on other, unidentified loops. The overall rate of RNA transcription on the giant loops is only about half that on the generality of other loops, and the RNA transcribed on the giant loops is computed to have a base ratio of approximately 25 A:39 C:9 G:27 U, implying that there must be about 4 times as many guanine residues on the transcribed as on the non-transcribed strand of the giant loops' DNA.