I. Overall Goals And Research Strategy This research is aimed at understanding the molecular mechanisms which regulate gene expression in mammalian cells. Two groups of genes in the mouse: those responsible for immunoglobulin production and a set of genes that encode some of the structural proteins of the ribosomes are being studied. The immunoglobulin genes belong to the class of so-called "luxury genes," which are expressed only in highly specialized tissues, in this case the B-lymphocyte. These genes are particularly interesting because their expression changes dramatically during the course of lymphocyte maturation, both in a qualitative and quantitative sense. The ribosomal (r) protein genes are categorized as "housekeeping genes." They are expressed in all types of tissue and are coordinately regulated according to the cells need for new ribosomes. Recombinant DNA methodology is used to isolate genes of interest and to produce appropriately modified derivatives of them. Gene organization and expression are examined by a variety of techniques, including DNA and RNA blots, nucleotide sequence analysis, transcriptional run-on and S1 nuclease protection assays, and appropriate transfection and transformation experiments with purified gene fragments. The knowledge gained by these studies should help establish some of the molecular bases for cellular differentiation and growth regulation.