Chromatin and transcriptional activity in early Xenopus development.

Experiments with Xenopus oocytes and embryos have determined a direct biochemical relationship between chromatin structure and transcription. Nucleosomes within specific nucleoprotein architectures can either activate or repress transcription. Developmentally regulated changes in chromosomal composition direct the dominant repression of specific genes. Reconstruction of chromatin templates in vivo establishes that replication-coupled chromatin assembly both represses basal transcription and facilitates a full range of inducible gene activity. Chromatin structure emerges as a major contributory factor to the regulation of genes.