GENETIC ELEMENTS WITHIN YEAST MITOCHONDRIAL AND MOUSE IMMUNOGLOBULIN INTRONS (SEQUENCE, ENHANCER, TECHNIQUE)

Chapter one discusses four possible intron functions and two genetic systems used for molecular analyses of such functions: the yeast mitochondrial cytochrome genes and the mouse immunoglobulin genes.

Chapter two describes mutations in two yeast mitochondrial cytochrome genes which lead to the abnormal accumulation of large transcripts from both genes and the absence of the mature mRNA species found in wild type strains. These findings suggest the involvement of two trans-acting elements in RNA splicing. This chapter appears as published in Cell 19, 1209-1215 (1979).

Chapter three shows that yeast mitochondrial deletion mutants, which lack the ability to carry out mitochondrial protein synthesis, have only precursor sized cytochrome b gene transcripts. We propose a model in which translation must extend from cytochrome b exons into in-phase intron reading frames. Each trans-acting intron could encode a fusion-protein which would be responsible for the splicing-out of its own intron in an autoregulatory manner. This chapter appears as published in Mobilization and Reassembly of Genetic Information, eds. Joseph, D. R., Schultz, J. J., Scott, W. A. and Werner, R. (Academic Press, New York), pp. 379-394 (1980).

Chapter four describes a procedure for sequencing genomic DNA directly from mammalian cells. We use this technique to analyze the methylation of cytosines in the mouse immunoglobulin heavy chain C(mu) gene. This chapter appears as published in the Proceedings of the National Academy of Sciences USA 81, 1991-1995 (1984).

Chapter five (work done in collaboration with Anne Ephrussi, Walter Gilbert and Susumu Tonegawa) describes further application of the direct genomic sequencing procedure to study the accessibility of DNA in the mouse heavy chain intron enhancer region to dimethyl sulfate in nuclei of various cell lines. Lymphoid cell specific effects are seen at two clusters of guanines separated by 125 bp. All known immunoglobulin enhancers contain regions similar in sequence to these sites. The consensus sequence is GCCAGGTGGC.