Intermediates in the synthesis of TolC protein include an incomplete peptide stalled at a rare Arg codon

TolC is a minor outer membrane protein of Escherichia coli K 12 and is initially synthesized as a precursor. A distinct intermediate polypeptide of Mr about 46 000 was consistently observed at the initial stages of biosynthesis. The further elongation of this peptide can be blocked by chloramphenicol. We have investigated the cause of the temporary accumulation of the 46 000-Mr intermediate and we postulate that the presence of a rare codon AGA (Arg) at codon 402 of the tolC mRNA halts translating ribosomes owing to a limiting amount of the tRNAArg (AGA) species in the cell. The translation of tolC mRNA can be increased by providing T4 tRNAArg (AGA), encoded on a plasmid.

A transposon-like element in human DNA

Mobile genetic elements have been reported in prokaryotes, plants, yeast and Drosophila. The only transposon-like sequences reported for mammalian organisms are closely related to retroviruses, although undoubtedly other transposon families exist within the mammalian genome. Although mobile genetic elements can only be identified as such if their mobility can be demonstrated in existing populations, transposon and transposon-like elements share several common biochemical and structural features. Here we demonstrate that a repetitive human sequence has many of the diagnostic features of transposable elements. This 2.3-kilobase (kb) transposon-like element contains two flanking long terminal repeat (LTR)-like 350-base pair (bp) repetitive sequences, each of which begins with the sequence 5' TG... and ends with ...CA 3'. The transposon-like element is bounded by 5-bp direct repeats. Discrete-length polyadenylated transcripts from HeLa cells are homologous to the transposon-like element. Members of this transposon-like family are found in extrachromosomal circular DNA molecules.

Biosynthesis of fredericamycin A, a new antitumor antibiotic

Fredericamycin A (FM A), produced by a strain of Streptomyces griseus, represents a new structural class of antitumor antibiotics containing a spiro ring system. Studies on the producer organism showed that glucose in the fermentation medium is not utilized until late in the growth stage, just prior to synthesis of FM A. [14C]Glucose tracer experiments demonstrated that glucose is incorporated into FM A by catabolism to acetate. Biosynthetic enrichment of FM A with single- and double-labeled [13C]acetate showed that the entire carbon skeleton of the spiro ring system is derived from acetate. L-Methionine was shown to provide the only nonskeletal carbon in FM A, the methoxy carbon at position C-6. The direction of the polyketide chain and the position of the carbon lost during biosynthesis were established by using stable isotope experiments. A general model for FM A biosynthesis is proposed, and a possible scheme for the formation of the spiro carbon center is presented.

Molecular characterisation of the Stc- mutation of Escherichia coli K-12

The previously described Stc- (suppressor of TolC) mutation modifies the phenotype of tolC mutants from OmpF- to OmpF+. Restriction mapping of chromosomal DNA from Stc+ and Stc- strains was performed to investigate the nature of the mutation which was shown to be a deletion, upstream of the ompC gene. DNA from the region of the deletion was cloned into pUC18 and a 650-bp PstI-EcoRI fragment was sequenced. The deletion started 49 bp upstream of the AUG start codon of the ompC gene, thus removing part of the ompC promoter and the whole of the micF gene. We suggest that the deletion of micF gives rise to the Stc- phenotype since the effect of micF expression is assumed to reduce ompF expression, and the Stc- phenotype involves increase in ompF expression.

Kpn I family of long-dispersed repeated DNA sequences of man: evidence for entry into genomic DNA of DNA copies of poly(A)-terminated Kpn I RNAs

We have isolated eight cDNA clones complementary to the human Kpn I repeat and determined the base sequence of three. We have also determined a portion of the base sequences of three human Kpn I family members. The three cDNA sequences are extensively homologous with the 3' ends of the three genomic Kpn I family members and with a simian Kpn I family member recently described [Thayer, R. E. & Singer, M. F. (1983) Mol. Cell. Biol. 6, 967-973]. The genomic repeats terminate in regions of sequence rich in dAMP residues close to sequences at the 3' ends of the cDNA clones; a precise 3'-terminal nucleotide cannot be distinguished. These structural features are consistent with the dispersal of at least some Kpn I family members by entry into genomic DNA of copies of Kpn I RNA transcripts. Each cDNA contains a long poly(dAMP) homopolymer at its 3' end and either one or two A-A-T-A-A-A polyadenylylation signal sequences upstream from it, suggesting that Kpn I family members may be transcribed by RNA polymerase II.

The TolC protein of Escherichia coli K12 is synthesised in a precursor form

We examined the biosynthesis of the TolC protein of Escherichia coli K12 in a pulse-chase experiment, followed by immunoprecipitation with anti-TolC antibody and SDS-PAGE of the immunoprecipitate. This showed that TolC protein was originally synthesised in a precursor form (Mr 54 500) which could be chased into the mature form (Mr 52 000). DNA sequencing of a portion of the cloned tolC gene showed that the N-terminus of the mature rotein was preceded by a typical signal sequence of 22 residues (Mr 2542). The initiator Met was preceded by a Shine-Dalgarno sequence, with the correct spacing.

Release of prostaglandins in experimental immunecomplex endophthalmitis and phacoallergic uveitis

Prostaglandins-E were demonstrated in the aqueous humour, the anterior uvea, and the choroid of rabbits in which type III allergic reactions were produced by two different methods. In general the levels of prostaglandins were found to be higher in those animals in which the immune complexes were formed from autologous rather than heterologous tissue antigens.

Electrolytes in surgical patients: the effect of pre-operative starvation and environmental temperature

Serum sodium, potassium and chloride values were measured before and after pre-operative starvation and after premedication in healthy subjects under going routine surgery, during both temperate and hot weather. No significant change in serum electrolytes occurred during temperate weather either after starvation or after premedication. In hot weather, when the subjects were sweating, a rise in serum electrolytes occurred, indicating fluid deficit of about 1-8 litres after a mean period of starvation of 11 hours; premedication with atropine and diazepam in these subjects was followed by a significant decrease in the serum electrolytes from the previous raised level after pre-operative starvation.

Incorporation of palmitate-1-14C into liver lipids of rats fed millet (Sorghum vulgarie) at different protein levels

Feeding of defatted millet <i>(Sorghum vulgarie) </i>at different protein levels to rats for 6 weeks caused significant increases in liver total lipids, cholesterol, fatty acids, triglycerides (TG), phospholipids and its two major fractions PC and PE, as compared to the controls. Plasma triglycerides in millet protein fed rats were not reduced. Incorporation of palmitate-1-¹⁴C into liver TG, PC and PE of millet protein fed rats was significantly greater than the controls. The incorporation of palmitate-1-¹⁴C into plasma TG and into liver FC and EC of rats fed millet protein was equal to or slightly increased as compared to controls. These results show that the accumulation of TG in liver of rats fed millet at different protein levels results from their greatly enhanced synthesis and unimpaired secretion into plasma.

Diversity, dominance, stability, and net production in the grasslands at Varanasi, India

A study conducted on the grassland of Varanasi (Tropical), has shown that species diversity increases productive efficiency of the ecosystem while dominance makes the system stable, though less efficient for production. These results are contradictory to McNaughton's observation that diversity decreases efficiency and generates community stability, and thus call for further work before generalization for all situations can be drawn.