The objective of the proposed research is to study the organization of immunogobulin(Ig) genes, their regulated expression through transcription, translation and the synthesis of Ig precursor to provide the two final products - circulating antibodies and the antigen-recognizing receptor on the surface of lymphoid cells. The L-chain precursor, which is the immediate product of mRNA translation, contains an N-terminal extra piece (19-22 residues long) which precedes the N-terminus of the mature protein. Our studies of Ig precursors have already provided new information on the structure of Ig-genes. These include: 1) the V-gene may be larger than hitherto realized; 2) Ig secretion may be regulated by the cleavage process in which the extra piece is removed to yield the mature L-chain; 3) the marked hydrophobicity of the extra piece may favor interaction of the precursor with cell membranes (endoplasmic membranes and cell-surface membrane); 4) independent expression of the C-gene, associated with translocation of the extra piece DNA from the V-gene to the C-gene. We plan to continue investigation of the structure-function relationship of the Ig precursor, and to extend the studies done on mouse myeloma L-chains to L- and H-chain of normal lymphocytes from mouse and other species. Another major objective is to study V- and C-genes in nuclear DNA, in order to decide between the germ line and somatic mutation hypothesis, provide direct evidence for possible translocation of V- and C-genes, and identify the location of the DNA coding for the extra piece. To these aims we shall prepare distinct nucleic acid probes for the V- and C-regions, by using the C-mRNA (recently purified in our laboratory) as well as whole L-chain mRNA, cDNAs, and appropriate nuclease-digests of hybrids formed between cDNAs and mRNAs of different subgroups. The distinct V- and C-region probes will be used to enumerate the V- and C-genes, and to localize these genes in restriction enzyme fragments of nuclear DNA from Ig producer and non producer cells.