[Electron microscopic study of transcription of loach oocyte ribosomal genes].

Transcription of ribosomal genes of a loach Misgurnus fossilis L. was studied by electron microscopy. Relative transcriptional activity in nucleoli at different vitellogenic stages was determined by direct calculation of the number of operating ribosomal genes in the nucleoli. Morphologic studies showed that the transcribing regions of mean length 2.3 +/- 0.2 mkm are separated by spacers of variable lengths. Both short (1.2--1.4 micrometer) and long (2.4--2.6 micrometer) spacers were visualised. The lateral RNP fibrils have granular structure, each granule containing 300--350 RNA bases. It was found that chromatin has nucleosomal structure in spacer regions and is of non-beaded, smooth structure in transcribing regions. The data obtained allow to suggest that in transcribing regions chromatin undergoes structural transition before the transcription process.