Transcription of "Lampbrush" chromosomes in a eukaryote

    The visible DNA strand is being transcribed by a series of closely-packed RNA polymerase (RNAPol) molecules moving serially along the strand. Each RNAPol is trailing a filament corresponding to an rRNA transcript. Note that the direction of transcription is towards the broad end of the "lampbrush": the longest filaments trail from an RNAPol that attached first.

    Lampbrush chromosomes are found in the oocytes of an amphibian, the European crested newt (Notopthalmus). Instead of condensing during meiotic prophase, they remained uncoiled so as to allow extensive transcription of rRNA genes to make the large number of ribosomes necessary for early development.  In this case, therefore, the RNA transcript is not translated.

Figure © 2004 by Griffiths et al. ; text © 2014 by Steven M. Carr