Chitosan is a natural cationic linear polymer that has recently emerged as an alternative nonviral gene delivery system. We have established the relationships between the structure and the properties of chitosan-pDNA polyplexes in vitro. Further, we have compared polyplexes of ultrapure chitosan (UPC) of preferred molecular structure with those of optimised polyethylenimine (PEI) polyplexes in vitro and after intratracheal administration to mice in vivo. Chitosans in which over two out of three monomer units carried a primary amino group formed stable colloidal polyplexes with pDNA. Optimized UPC and PEI polyplexes protected the pDNA from serum degradation to approximately the same degree, and they gave a comparable maximal transgene expression in 293 cells. In contrast to PEI, UPC was non toxic at escalating doses. After intratracheal administration,

Fed-batch production of recombinant beta-galactosidase in E. coli was studied with respect to the specific growth rate at induction. The cultivations were designed to induce protein production by IPTG at a glucose feed rate corresponding to high mu = 0.5 h(-1)) or low (mu = 0.1 h(-1)) specific growth rate. Protein production rate was approximately 100% higher at the higher specific growth rate, resulting in the accumulation of beta-galactosidase up to 30% of the total cell protein. Transcription analysis showed that beta-galactosidase-specific messenger RNA was immediately formed after induction (<5 min), but the amount was the same in both cases and was thus not the initial limiting factor. The content of ribosomes, as represented by rRNA, rapidly decreased with specific growth rate from a relative level of 100%, at the high specific growth rate, to 20% at the low specific growth rate. At high specific growth rate, ribosomes were additionally degraded upon induction due to the high production level. Translation therefore seemed to be the initial limiting factor of the protein synthesis capacity. The alarmone guanosine tetraphosphate increased at both high and low feed level inductions, indicating an induction-forced starvation of charged tRNA and/or glucose. The altered physiological status was also detected by the formation of acetic acid. However, the higher production rate resulted in high-level accumulation of acetic acid, which was absent at low feed rate production. Acetic acid production is thus coupled to the high product formation rate and is proposed to be due either to a precursor drain of Krebs cycle intermediates and a time lag before induction of the glyoxalate shunt, or to single amino acid overflow, since the model product is relatively poor in glycin and alanin. In conclusion, it is proposed that production at high specific growth rate becomes precursor-limited, while production at low specific growth rate is carbon- and/or energy-limited.

Mutations in the two genes for EF-Tu in Salmonella typhimurium and Escherichia coli, tufA and tufB, can confer resistance to the antibiotic kirromycin. Kirromycin resistance is a recessive phenotype expressed when both tuf genes are mutant. We describe a new kirromycin-resistant phenotype dominant to the effect of wild-type EF-Tu. Strains carrying a single kirromycin-resistant tuf mutation and an error-restrictive, streptomycin-resistant rpsL mutation are resistant to high levels of kirromycin, even when the other tuf gene is wild type. This phenotype is dependent on error-restrictive mutations and is not expressed with nonrestrictive streptomycin-resistant mutations. Kirromycin resistance is also expressed at a low level in the absence of any mutant EF-Tu. These novel phenotypes exist as a result of differences in the interactions of Resistance to the antibiotic streptomycin can be conferred by mutations in ribosomal protein or rRNA. High-level resistance is conferred by mutations in the ribosomal protein gene rpsL (4,19). The structural basis for resistance or sensitivity to streptomycin is unknown. Some rpsL mutations result in streptomycin-resistant ribosomes which restrict the level of translational errors (6, 10). Error restriction is associated with an increased proofreading of the EFTu tRNA ternary complexes by the mutant ribosomes (5).We selected an error-restrictive kirromycin-resistant mutant strain in the expectation that it would harbor a novel tuf mutation. Surprisingly, we found that the phenotype is conferred by the combined effects of separate mutations in the ribosome and one of the tufgenes. Here we describe the origins of this complex phenotype. MATERIALS AND METHODSBacterial and phage strains. The bacterial strains used are listed in Table 1. S. typhimurium strains were derivatives of LT2. All transductions in S. typhimurium were made with P22 HT105/1 int-201 (21). The strain TH139 (trpE91 tufA8 hisA&644 zee-1::TnlO) was transduced with phage grown on hisG3720, selecting for growth on histidinol and screening for tetracycline sensitivity, to make TH488. The tufA8 * Corresponding author. mutation suppresses both trpE9l and hisG3720 (15) (5,6,10) were transduced into a derivative of MG1655, US428 (aroE zhd-126::TnlO), by selecting for prototrophy and screening for tetracycline sensitivity and streptomycin resistance.Media. Liquid and solid media were rich LB and minimal M9 media as described previously (13,17). Kirromycinresistant mutants were selected and checked on LC plates (27) containing 2 mM EDTA (pH 8.0). Media contained, as appropriate, tetracycline (15 ,ug/ml), kanamycin (50 pug/ml), streptomycin (100 ,ug/ml), or mocimycin (kirromycin) (100 3635

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We have used quantitative immunoblotting to estimate the amount of EF-Tu in a variety of S. typhimurium strains with wild-type, mutant, insertionally inactivated or plasmid-borne tuf genes. In the same strains we have measured translation elongation rate, exponential growth rate and the level of nonsense codon readthrough. In the wild-type strain, at moderate to fast growth rates, our data show that EF-Tu makes up 8-9% of total cell protein. Strains with either of the tuf genes insertionally inactivated have 65% of the wild-type EF-Tu level, irrespective of which tuf gene remains active, or whether that gene is wild-type or a kirromycin-resistant mutant. Strains with only one active tuf gene have reduced growth and translation elongation rates. From the magnitude of the reduction in elongation rate relative to the level of EF-Tu we calculate that in glucose minimal medium the in vivo saturation level of wild-type ribosomes by ternary complexes is only 63%. Strains with a ribosome mutation causing a poor interaction with ternary complex are non-viable on minimal medium when the level of EF-Tu is reduced.