The expression of heat shock genes in Drosophila embryos and cultured cells is being investigated at the levels of both primary transcription and post-transcriptional hnRNA processing. Heat shock gene transcripts will also be isolated as hnRNP particles using cloned heat shock DNA affinity probes, and their nucleoprotein structure will be analyzed. The overall objectives are to (1) explore the relative contributions of transcriptional vs. post-transcriptional controls to a rapidly changing cytoplasmic mRNA repertoire and (2) to advance our understanding of the relationships between gene transcription and nuclear structure.