A rapid and efficient method for targeted random mutagenesis

Genetic analysis of the structure and function of RNase P from E. coli

A brief review of the genetic studies on ribonuclease P (RNase P) from Escherichia coli is presented. Temperature-sensitive mutants of E. coli defective in tRNA processing were isolated by screening cells which were unable to synthesize a suppressor tRNA at restrictive temperature. Structural analysis of accumulated tRNA precursors showed that the isolated mutants were defective in RNase P activity. Analyses of the mutants revealed that the enzyme is essential for the synthesis of all tRNA molecules in cells and that the enzyme consists of two subunits. Analyses of the isolated mutants revealed a possible domain structure of the RNA subunit of the enzyme.

Functional domains of the penicillinase repressor of Bacillus licheniformis

The penicillinase repressor (PENI) negatively regulates expression of the penicillinase gene (penP) in Bacillus licheniformis by binding to its operators located within the promoter region of penP.penI codes for a protein with 128 amino acids. Filter-binding analyses suggest that the active form of the repressor is a dimer. Genetic analyses of PENI derivatives showed that the repressor carrying either a 6-amino-acid deletion near the N terminus or a 14-amino-acid deletion at the C terminus was functionally inactive in vivo. A repressor derivative carrying a 6-amino-acid deletion within its N-terminal region was extensively purified and used in DNA footprinting and subunit cross-linking analyses. The results of these studies showed that the repressor derivative had lost its ability to bind operator specifically even though it could dimerize effectively. In similar studies, we demonstrated that an N-terminal portion of PENI with a molecular mass of 10 kDa derived by digestion with papain was able to bind operator specifically but with reduced affinity and had completely lost its ability to dimerize. These data suggest that the repressor has two functional and separable domains. The amino-terminal domain of the repressor is responsible for operator recognition, and the carboxyl-terminal domain is involved in subunit dimerization.

The cooperative interaction between two motifs of an enhancer element of the chicken alpha A-crystallin gene, alpha CE1 and alpha CE2, confers lens-specific expression

An 84 bp element located between nucleotides -162 and -79 of the chicken alpha A-crystallin gene exhibits lens-specific enhancer activity. Transient transfection experiments using 5' deletion and linker scanner mutants has indicated that the 84 bp enhancer element is composed of three motifs, alpha CE1 (-162 to -134), alpha CE3 (-135 to -121) and alpha CE2 (-119 to -99). Neither alpha CE1 or alpha CE3 motif alone can exhibit enhancer activity even when trimerized, whereas together they can direct some degree of lens-specific expression. alpha CE2 alone shows low transcriptional activity when trimerized. A combination of alpha CE1 with alpha CE2 exerts full lens-specific enhancer activity comparable with that of the 84 bp enhancer element, indicating that alpha CE1 and alpha CE2 motifs are sufficient to confer lens-specific expression. Transcriptional activation by these two motifs from a distance required the additional presence of either or both motifs adjacent to the beta-actin basal promoter. Gel shift experiments indicated that the alpha CE1, alpha CE2 and alpha CE3 motifs specifically bind nuclear proteins. alpha CE1 binds a protein predominantly present in lens cells, whereas alpha CE2- and alpha CE3-binding proteins differ between lens and lung cells. Mutations within the alpha CE1 and alpha CE2 motifs that failed to bind nuclear factors in vitro resulted in loss of transcriptional activation, indicating that these nuclear factors play a key role in controlling lens-specific expression.

The ADE2 gene from Saccharomyces cerevisiae: sequence and new vectors

We have determined the sequence of a DNA fragment encoding the ADE2 gene from Saccharomyces cerevisiae. A DNA fragment of 2241 bp capable of complementing ade2 mutations was modified so it is available as a single BglII fragment for use in yeast vectors or for gene disruptions. The minimal fragment codes for a putative protein which is highly similar to the protein encoded by the ADE6 gene from Schizosaccharomyces pombe and to the proteins encoded by the purEK operon of Escherichia coli.