D. Swan

Processed genes: a dispersed human immunoglobulin gene bearing evidence of RNA-type processing

A dispersed immunoglobulin pseudogene carries two hallmarks of RNA processing—spliced J and C regions and a poly (A)-rich tail. Its discovery strengthens the notion that processed genes are a significant feature of the mammalian genome and that genetic information can return to the genome via an RNA intermediate.

THE ORGANIZATION AND DIVERSITY OF IMMUNOGLOBULIN κ AND λ GENES

Abstract: Our studies have focused on several hypotheses put forward to account for the diversity of immunoglobulin genes. These studies have shown that the constant regions of the mouse κ and λ chains are represented as relatively unique sequences in the genome of the mouse. Experiments which have attempted to focus on the genetic representation of the variable region of the κ chain are not as readily interpreted. They do, however, rule out thousands of closely related germ line sequences. As a result of ambiguities in the κ system, we have turned our attention to a simpler model, the mouse λ light chain. Since detailed analyses have shown that there are at least seven very closely related λ light chains, this class provides a very useful model for studies involving molecular hybridization. Utilizing mouse λ chain 3 H-cDNA, hybridization kinetic analyses indicate that these sequences are represented among the relatively unique genetic sequences in the mouse genome. This result tends to rule out a germ line model for antibody diversity. The reservations with respect to reaching such a conclusion are also discussed.

THE ORGANIZATION OF IMMUNOGLOBULIN GENES

ABSTRACT In order to distinguish among various models which have been advanced to account for the diversity of antibody molecules, we must know how the constant and variable regions of immunoglobulins are represented in the somatic genome. For this purpose, we have purified mRNA corresponding to a mouse kappa immunoglobulin light chain from the myeloma tumor, MOPC-41. This mRNA directs the enzymatic synthesis of highly radioactive DNA (cDNA). This cDNA, which should correspond to the constant region of the kappa chain, was assessed for reiteration frequency using hybridization kinetic analysis and was found to be represented approximately three times per haploid genome . This result tends to rule out germ line hypotheses which require many copies of the constant region gene. It also requires the postulation of a recombinational mechanism to join constant and variable region sequences. Hybridization kinetic analyses designed to assess the entire light chain sequence (C and V regions) made use of 125I-MOPC-41 mRNA. These revealed a major component of relatively unique frequency and a minor (~ 20%) component with a reiteration frequency of approximately 30-50 copies per haploid genome. Careful analysis of the extent of hybridization of this mRNA to DNA prepared from several tumors and tissues, thermal profiles, and relevant competition studies, while sensitive, do not permit us to distinguish unambiguously between a germ line model and the type of somatic mutation model which permits germ line genes corresponding to each kappa subgroup. Our results do, however, clearly rule out the existence of thousands of variable region sequences so closely related to the MOPC-41 V-region as to permit extensive, stable cross hybridization.

DNA Complementary to Globin and Immunoglobulin mRNA: A Probe to Study Gene Expression

During the development of an embryo, various processes occur which induce the formation of differentiated tissues. Some of these processes can be observed at a molecular level, for example, myosin is synthesized in muscle cells, crystaline in lens tissue, keratin in skin, immunoglobulin in lymphocytes and hemoglobin in reticulocytes (1,2).