Biomedical subjects
Publications and source records attributed to M B Rotheim.
IncN group plasmids, including pCU1, are able to kill Klebsiella pneumoniae when conjugatively transferred from an Escherichia coli donor. Transposon mutagenesis and deletion analysis of the known tra complementation groups were used to demonstrate that the tra gene products inactivated are not required for the Kik phenotype.
Tetrahymena ciliary membrane vesicles are shown to interact with preconjugant cells in a mating type-specific way. When cells are treated with vesicles of a different mating type before mixing for conjugation, cell pairing is enhanced, and the normal prepairing period is partially eliminated. This enhancement is mating type specific since it is not observed after pretreatment of cells with vesicles of their own mating type. In contrast, when vesicles are added at the time of mixing of two starved cultures, cell pairing is delayed in a concentration-dependent manner. By varying the conditions, we demonstrated enhancement or inhibition, or both. These results are interpreted in terms of two independent interactions of cells with vesicles. We suggest that first, vesicles substitute for another cell in cell-cell prepairing interaction and second, vesicles compete for adhesion sites produced during the prepairing period. Finally, the data presented are summarized within a speculative framework that calls attention to potential analogies with hormone-receptor signaling in mammalian cells.
We examined the effect of inhibitors of receptor-mediated endocytosis on cell pair formation during conjugation in Tetrahymena thermophila. Dansylcadaverine (20 microM), methylamine (20 mM), and bacitracin (2 mg/ml) prevented cell pair formation even when added poststarvation, after mixing of cells of opposite mating types (during the preparing interaction). Chloroquine (10 and 25 microM) did not inhibit cell pair formation, leading to the conclusion that inhibition by dansylcadaverine, methylamine, and bacitracin is not due to an alkalinization of the lysosome. These results did not allow us to define the time in the preparing interaction at which inhibition occurs, nor to identify the cellular components involved, but they did support the hypothesis that an endocytotic event(s) plays a role in the cell contact-mediated recognition which occurs during the preparing interaction.
Polyacrylamide gel electrophoresis of the 30S ribosomal proteins derived from six streptomycin resistant strains indicates that each mutation alters the same ribosomal protein (str-r protein). Preliminary data utilizing SDS gels indicates that the str-r protein has a molecular weight between 10,000 and 20,000 daltons. No significant differences could be detected between the molecular weight of the str-r protein when it is derived either from a sensitive or from a resistant strain, including those derived from strains carrying multisite mutations of different genetic size. We have estimated the size of the multisite str-r mutations to be less than 30 base pairs. Two factor crosses with str-r markers in the trans position demonstrate recombination frequencies expected of closely linked, intragenic markers although cotransfer frequencies, of these same markers from the cis position, are very low. It is concluded that the cotransfer frequencies represent a marker effect and possible explanations are discussed. A reinterpretation of the genetic map of the pneumococcal str-r locus is presented.
The altered growth of a pneumococcal mutant containing marker M, which confers ability to utilize mannitol, and a modifier gene is reported. The modifier gene is closely linked to the M gene and imposes a requirement for growth in 0.4% glucose before growth in mannitol medium. The tentative position of the M gene of pneumococcus is ery-r str-r M sul-rd.
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