Some ultrastructural aspects of genetic activity in eukaryotes.

A brief overview is given of the types of information that have been obtained by chromatin spreading methods regarding the ultrastructure and regulation of genetic units. The examples used are: ribosomal RNA genes of the spotted newt; the silk fibroin gene of Bombyx mori; chorion gene amplification in Drosophila melanogaster; RNA synthesis patterns during early embryogenesis of D. melanogaster; regulation of transcription on homologous non-ribosomal transcription units of D. melanogaster; specific nascent transcript cleavage in insects; and nascent polypeptides on insect polyribosomes. The conclusion is drawn that further innovations will be required before significant advances in the use of chromatin spreading techniques to study ultrastructural aspects of genetic activity can occur.