Synthesis of part of a mouse immunoglobulin light chain in a bacterial clone

Expression of a nitrogen-fixation gene encoding a nitrogenase subunit in yeast

Biological nitrogen fixation is catalyzed by nitrogenase, an enzyme complex exclusive to prokaryotes. We used the yeast Saccharomyces cerevisiae to study the synthesis, and subsequently the assembly, of nitrogenase components in a eukaryote. Here, the Klebsiella pneumoniae nifH gene, encoding the subunit of the Fe protein (Kp2) component of nitrogenase, was expressed in S. cerevisiae from the yeast ADHI promoter. The nifH gene product, detected in yeast by immunoblot analysis with anti-Kp2 antibodies, exhibited the same electrophoretic mobility in SDS-polyacrylamide gels as that of the Kp2 subunit synthesized in K. pneumoniae. Estimates of Kp2 antigen and assays of beta-galactosidase activity specified by nifH'-'lacZ fusions showed that the level of nifH product was similar in anaerobically and aerobically grown yeast, but varied with different transforming plasmids and in various haploid and diploid yeast strains. A cistron located downstream to nifH in a transcript resembling the polycistronic mRNA of the nifHDKY operon in K. pneumoniae is not translated in yeast.

Assembly of functional antibodies from immunoglobulin heavy and light chains synthesised in E. coli

Genes for a murine mu heavy chain and a lambda light chain immunoglobulin have been inserted into bacterial expression plasmids containing the Escherichia coli trp promoter and ribosome binding site. Induction of transcription from the trp promoter results in accumulation of both light and heavy chain polypeptides in appropriate host strains. Both proteins were found as insoluble products. Following extraction and purification of the immunoglobulin containing fractions, antigen binding activity was recovered. The activity demonstrates essentially the same properties as the antibody from the hybridoma from which the genes were cloned.

Secretion and processing of an immunoglobulin light chain in Escherichia coli

When a cDNA coding for the kappa light chain (L-321) from the mouse MOPC321 myeloma was cloned into Escherichia coli, L-321 antigens were found in both cytoplasmic and periplasmic fractions. In cells synthesizing the intact chain, starting with its signal peptide, the periplasm contained a mature-size immunoglobulin indicating that the eukaryotic signal peptide can initiate secretion and be processed. When the entire cDNA for L-321 (including its signal peptide) was inserted in the gene for bacterial beta-lactamase, processing cleaved only the first bacterial signal sequence of the hybrid protein synthesized. Removal of the beta-lactamase signal peptide was also observed with another beta-lactamase-L-321 hybrid which did not include the immunoglobulin signal peptide and the adjacent part of the variable region. The two hybrid proteins may, however, differ in their mode of secretion.

A cloned immunoglobulin cDNA fragment enhances transposition of IS elements into recombinant plasmids

Evidence is presented indicating that a novel DNA sequence arrangement generated by in vitro recombination may elicit high frequency transpositions of IS elements. A 109 bp Bam HI fragment of the cDNA for the immunoglobulin kappa light chain from MOPC 321 myeloma was cloned into the Bam HI site of pBR313. The cloned fragment extends from the codon for Gly 57 to the V-J junction. Insertions of IS1 or IS5 were identified in 6 of 50 plasmid DNAs isolated from freshly transformed clones. Additional transposition events were detected after subculturing for several growth cycles. Three independent insertions of IS1 occurred in the promoter region of the TcR operon. All IS5 and the remaining IS1 insertions were located in the TcR region upstream to the cloned DNA sequence. Sequences homologous to the ends of IS1, or corresponding to the consensus sequence at the target site of IS5 are present near the estimated sites of insertion of IS1 or IS5 respectively. Bacteria harboring recombinant plasmids carrying the cloned DNA in either orientation grew at a reduced rate relative to cells harboring pBR313, suggesting that fused gene products made from the two types of plasmid were inhibitory to cell growth. IS insertions, which relieved this inhibitory effect and thereby provided a selective advantage, were found exclusively in plasmids carrying the cloned DNA in only one of the two orientations. The fact that IS elements were not observed in the other type of recombinant plasmid indicates that selective pressure alone is not sufficient to account for the frequent IS insertions observed and that sequences at a distance from the site of IS insertion may be critical in the regulation of transposition frequency.

Sensitive immunological detection of translation products in SV40 plaques

A simple and sensitive in situ radioimmunoassay, using simian virus 40 (SV40) proteins as a model, has been developed for the detection of specific translation products of foreign genes cloned in viral vectors. This assay is based on the coupling of all proteins in viral plaques to diazophenylthioether (DPT)-paper. Specific proteins bound to the filter are detected by autoradiography after sequential incubation with (i) unfractionated and unlabeled specific antiserum and (ii) 125I-labeled protein A from Staphylococcus aureus. This assay detects SV40-specific proteins in individual plaques as early as 42 h after infection and its sensitivity limit is below 5 x 10(8) molecules of the major SV40 capsid protein, VP1.