Transforming growth factor beta 1 inhibition of p34cdc2 phosphorylation and histone H1 kinase activity is associated with G1/S-phase growth arrest.

Transforming growth factor beta 1 (TGF beta 1) is a potent inhibitor of epithelial cell proliferation. We present data which indicate that epithelial cell proliferation is inhibited when TGF beta 1 is added throughout the prereplicative G1 phase. Cultures become reversibly blocked in late G1 at the G1/S-phase boundary. The inhibitory effects of TGF beta 1 on cell growth occur in the presence of the RNA synthesis inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole. Associated with this inhibitory effect is a decrease in the phosphorylation and histone H1 kinase activity of the p34cdc2 protein kinase. These data suggest that TGF beta 1 growth inhibition in epithelial cells involves the regulation of p34cdc2 activity at the G1/S transition.     

Levels of ribosomal protein S1 and elongation factor G in the growth cycle of Escherichia coli.

The relative levels of ribosomes, ribosomal protein S1, and elongation factor G in the growth cycle of Escherichia coli were examined with two-dimensional polyacrylamide gel electrophoresis. Nonequilibrium pH gradient polyacrylamide gel electrophoresis was used in the first dimension, and polyacrylamide gradient-sodium dodecyl sulfate gel electrophoresis was used in the second dimension. The identities of protein spots containing S1 and elongation factor G were confirmed by radioiodination of the proteins and peptide mapping of the radiolabeled peptides. The levels of ribosomes and ribosomal protein S1 were coordinately reduced during transition from exponential phase to stationary phase. There was no accumulation of S1 in the stationary phase. In marked contrast, the level of elongation factor G showed no significant change from exponential phase to stationary phase. The relative level of elongation factor G compared with ribosomes or S1 increased by about 2.5-fold during transition from exponential phase to stationary phase. The results show that there are differences between the regulation of the levels of elongation factor G and of ribosomal proteins, including S1, apparent during the transition from exponential to stationary phase.     

Analysis of tetracycline resistance encoded by transposon Tn10: deletion mapping of tetracycline-sensitive point mutations and identification of two structural genes

Deletions in the tet genes derived from Tn10 were formed from different tet::Tn5 insertion mutations by removing DNA sequences located between a HindIII site in Tn5 and a HindIII site adjacent to the tet genes. Tetracycline-sensitive point mutations were mapped in recombination tests with the deletions and were thus aligned with the genetic and physical map of the tet region. Plasmids carrying point mutations were tested for complementation with derivatives of pDU938, a plasmid carrying cloned tet genes derived from Tn10 which had been inactivated by Tn5 insertions. Complementation occurred between promoter-proximal tet point mutations and distal tet::Tn5 insertions, suggesting the existence of two structural genes, tetA and tetB. These results, together with the analysis of polypeptides in minicells harboring pDU938tet::Tn5 mutants, suggested that tetA and tetB are expressed coordinately in an operon. The tetB gene encodes the previously characterized 36,000-dalton cytoplasmic membrane TET protein, but the product of tetA was not identified. Point mutations in either tetA or tetB led to the defective expression of the resistance mechanism involving tetracycline efflux. It is suggested that the tetA and tetB products interact cooperatively in the membrane to express resistance.     

Uptake and dissimilation of glycerol by wild type and glycerol nonutilizing strains of Neurospora crassa

Summary Seven mutant strains defective for utilization of glycerol, glyceraldehyde or dihydroxyacetone were isolated. One strain was deficient for NAD-linked glycerol-3-phosphate dehydrogenase, two for glycerol kinase, and four had no detected enzymatic deficiency, although one of the latter strains was deficient in glycerol uptake. Glycerol uptake was increased by incubation in glycerol, glycerol-3-phosphate, erythritol, and propanediol, and was protein-mediated below 0.14 mM glycerol, but at higher concentrations free diffusion predominated. Glycerol uptake was decreased by cycloheximide and was more sensitive to sodium azide than to iodoacetate.     

Effect of β-Propiolactone on Sendai Virus

The biological properties (infectivity, hemagglutination, hemolysis, cell fusion, neuraminidase) of Sendai virus were dissociated on the basis of sensitivity to beta-propiolactone, by freeze-thawing, by heating at different temperatures, and by adsorption-elution with formalinized chicken erythrocytes. Possible mechanisms whereby beta-propiolactone selectively destroys viral infectivity are discussed.     

Phytochrome control of short-day-induced bud set in black cottonwood

In trees and other woody perennial plants, short days (SDs) typically induce growth cessation, the initiation of cold acclimation, the formation of a terminal bud and bud dormancy. Phytochrome control of SD-induced bud set was investigated in two northern clones of black cottonwood (Populus trichocarpa Torr. & Gray) by using night breaks with red light (R) and far-red light (FR). For both clones (BC-1 and BC-2), SD-induced bud set was prevented when R night breaks as short as 2 min were given in the middle of the night. When night breaks with 2 min of R were immediately followed by 2 min of FR, substantial reversibility of bud set was observed for BC-1 but not for BC-2. By comparing the effects of the R night breaks on bud set and the length of specific internodes, we determined that the R night breaks influenced internode elongation in two opposing ways. First, the addition of a R night break to the SD treatment prevented the cessation of internode elongation that is associated with bud set. Those internodes that would not have elongated under SDs (and would have been found within the terminal bud) elongated in the R treatment. Second, the R night breaks decreased internode length relative to the long-day (LD) control. In contrast to the clonal differences in reversibility that we observed for bud set, the decrease in internode length (i.e. the second effect of R) was R/FR reversible in both clones. Based on these results, we conclude that internode elongation is influenced by two distinct types of phytochrome-mediated response. The first response is a typical response to photpperiod, whereas the second response is a typical “end-of-day” response to light quality. Our results demonstrate that SD-induced bud set in black cottonwood is controlled by phytochrome but that clonal differences have an important influence on the R/FR reversibility of this response. The availability of an experimental system in which SD-induced bud set is R/FR reversible will be valuable for studying the physiological genetics of photoperiodism in trees.