Evolution ofE.coli tRNATrp

Earlier studies (1) have shown there are direct correlations between the hydrophobicity ranking of most amino acids and their anticodonic nucleotides. However, four anticodonic assignments, i.e. those for Trp, Tyr, Ile and the XGA anticodons for Ser, did not correlate. It was our proposal that this failure to correlate was due to the fact that these assignments were made late, relative to the bulk of the assignments, in evolution through the mutation of existing tRNAs. We have shown (2) thatE. coli tRNA^{Ile 1} and tRNA^{Ile 2} were likely derived from tRNA^{Val 1} and tRNA^Lys respectively andE. coli tRNA^Tyr was possibly derived fromE. coli 5s rRNA or a common precursor with 5s rRNA (3). The fact that quite high homologies were observed in these comparisons is consistent with the late evolution of the tRNAs in question. We now examine the evolution ofE. coli tRNA^Trp by comparing its homology with otherE. coli tRNAs. The data suggest a possible evolutionary relationship withE. coli tRNA^Gly or tRNA^Arg. The data support the idea of the late assignment of anticodons to Trp.Deceased.     

Electrophysiology of a chick neuronal nicotinic acetylcholine receptor expressed in Xenopus oocytes after cDNA injection

Brain nicotinic acetylcholine receptors (nAChRs) are made up of protein subunits that differ from those constituting muscle nAChRs. To characterize the physiological properties of one class of avian brain nicotinic receptor, we injected the nuclei of Xenopus oocytes with full-length cDNAs for the ligand binding (alpha 4) and structural (n alpha) subunits. Injected oocytes had large ACh-induced currents in the microampere range that were insensitive to alpha-bungarotoxin, as expected for neuronal nAChRs. We found that these brain nAChRs incorporate at least two alpha 4 subunits and that their functional properties differ from muscle nAChRs in at least two respects: the elementary conductance is considerably smaller (20 pS), and channels in outside out patches stop functioning within a few minutes.     

Isolation and physiological study of an amylolytic strain of Lactobacillus plantarum

Summary An amylolytic lactic acid bacterium identified as Lactobacillus plantarum was isolated from cassava roots (Manihot esculenta var. Ngansa) during reting. The amylolytic enzyme synthesized was an extracellular -amylase with an optimum pH of 5.0 and an optimum temperature of 55° C. Cultured on starch, the strain displayed a growth rate of 0.43 h^–1, a biomass yield of 0.19 g·g^–1 and a lactate yield of 0.81 g·g^–1. The growth kinetics were similar on starch and glucose. Sufficient enzyme was synthesized and starch hydrolysis was not a limiting factor for growth. Biosynthesis of the enzyme was observed when the glucose concentration was less than 6.7 g·l^–1 and reached up to 4 IU·ml^–1 at the end of the fermentation. Offprint requests to: M. Raimbault     

The gene for the alpha i1 subunit of human guanine nucleotide binding protein maps near the cystic fibrosis locus.

The gene for the alpha i1 subunit of human guanine nucleotide binding (G) protein was mapped by in situ hybridization to chromosome 7 at band q21. The regional chromosomal location of the human alpha i1 gene was confirmed using human/mouse somatic-cell hybrid lines containing portions of human chromosome 7. Because the alpha i1 gene mapped near the cystic fibrosis locus and because an abnormal G protein might be expected to contribute to the pathophysiology of this disease, the alpha i1 gene was mapped with respect to the cystic fibrosis locus as defined by the Met oncogene and anonymous DNA marker pJ3.11. The location of the alpha i1 gene proved to be distinct from that of the cystic fibrosis locus.     

Calcitonin and vasopressin affect epithelial properties in a renal cell line

We have used a stable clonal variant (D + Sc), isolated from the LLC-PK1 pig kidney-derived cell line and selected for its extensive capacity to form domes, in order to study the hormonal modulation of epithelial permeability in culture. Calcitonin, vasopressin, and other agents that raise intracellular adenosine 3',5'-cyclic monophosphate levels caused a rapid and dramatic decrease in the size and number of domes. This effect was independent of RNA and protein synthesis, and thus appeared unrelated to the production of urokinase, a proteinase synthesized by the cells in response to these agents. Calcitonin caused a decrease in transepithelial electrical resistance, suggesting that the effect of the hormone on domes was due to an increase in the permeability of a paracellular pathway. Thus, in addition to the wellknown effects of vasopressin on collecting duct permeability, part of the in vivo effect(s) of calcitonin and vasopressin on the renal tubule might also involve alterations of epithelial permeability related to those described here.     

Correlates and implications of breast-feeding practices in Bas Zaire

A sample of 1871 women having a child under 3 years old in Bas Zaire was studied to determine the correlates of breastfeeding practices and to examine the interrelationships among breastfeeding, contraceptive practices and desire for pregnancy. The methods of analysis applied were life table analysis and its multivariate extensions. Most of the findings in this analysis are consistent with current literature on the correlates of the duration of breastfeeding. Maternal education, economic status, age, parity, urban residence, pregnancy, and sex of the index child were significantly related to the length of breastfeeding. Among non-pregnant women, current desire for pregnancy was also related to breastfeeding status when the length of time since birth of the last child was taken into consideration. Rural women were reportedly ready for another pregnancy sooner after the birth of their last child than were urban women. Breastfeeding appears to be the most important means of contraceptive protection in the study population. The effective traditional method of extended postpartum abstinence is not widely prevalent, particularly among the urban sample, and indeed seems to be on the decline. The data presented here also suggest that breastfeeding pratices are changing in this area of Africa where little economic development has occurred in the past 20 years. This research suggests that if current trends continue, fertility levels are likely to increase significantly. The findings also indicate that Bas Zairian mothers want to space their births and for this reason may be receptive to family planning programs that use appropriate strategies.     

Long-term comparative effect of cholecystokinin and gastrin on mouse stomach, antrum, intestine, and exocrine pancreas

Mice were injected three times a day for 12 days with 300 micrograms/kg body weight of gastrin G17 or 37.5 Ivy dog U/kg body weight of CCK or saline. Other mice were also injected four times an hr for 1 hr with 7.5 micrograms/kg of gastrin, nine Ivy dog U/kg of CCK or saline; 1 hr before killing, they were injected with tritiated thymidine to evaluate the labelling indices in peptic, antral, duodenal, jejunal, and ileal mucosae. Four hours after the first injection of the two peptides, the peptic labelling indices increased while those of intestinal mucosa increased 8 hr after these injections. Long-term injections of CCK had a trophic effect on secretory cells of the digestive tract: the number of gastric zymogenic cells, Paneth cells, and the mucous cells of Brünner glands were hypertrophied. The pepsin, amylase, chymotrypsin, and lysozyme activities increased in stomach, exocrine pancreas, and intestine, respectively. Neither parietal cells nor intestinal enterocytes and hydrolase activities were affected. The trophic effect of long-term injections of gastrin is confirmed on parietal cells and exocrine pancreatic parenchyma and is demonstrated in Paneth cells. Confirming cytological results, pancreatic lipase and amylase activities and intestinal lysozyme activity were increased after gastrin. Although CCK and gastrin have a structural analogy, these two peptides did not affect the same cellular types. A specific action of CCK on the main secretory cells of the digestive mucosa is demonstrated.     

Characterization of Rhizobia from Ineffective Alfalfa Nodules: Ability to Nodulate Bean Plants [Phaseolus vulgaris (L.) Savi.]

This study was initiated to characterize Rhizobium isolates obtained from root nodules of ineffectively nodulated, field-grown alfalfa (Medicago sativa L.) plants. The purpose was to determine if these isolates possessed characteristics which would explain either their ineffectiveness in N₂ fixation or their apparent ability to tolerate the moderately acid soil conditions from which they originated. Isolates were characterized by analysis of growth rate, 39°C tolerance, acid production on conventional media, and symbiotic performance. All isolates were ineffective in N₂ fixation on alfalfa, and they contained one or more anomalous characteristics. These included either slow growth rate, lack of 39°C tolerance, or lack of acid production on conventional media. Infectiveness tests on a broad range of legumes revealed that the isolates formed root nodules on M. sativa, Medicago lupulina L., and Phaseolus vulgaris (L.) Savi. (common bean). These results provide evidence that, in some situations, ineffective nodulation of M. sativa in the field may be due to the presence of promiscuous, native Rhizobium species.     

Vinculin in subsarcolemmal densities in chicken skeletal muscle: localization and relationship to intracellular and extracellular structures

Using immunocytochemical methods we have studied the distribution of vinculin in the anterior and posterior latissimus dorsi skeletal (ALD and PLD, respectively) muscles of the adult chicken. The ALD muscle is made up of both tonic (85%) and twitch (15%) myofibers, and the PLD muscle is made up entirely of twitch myofibers. In indirect immunofluorescence, antivinculin antibodies stained specific regions adjacent to the sarcolemma of the ALD and PLD muscles. In the central and myotendinous regions of the ALD, staining of the tonic fibers was intense all around the fiber periphery. Staining of the twitch fibers of both ALD and PLD muscles was intense only at neuromuscular junctions and myotendinous regions. Electron microscopy revealed subsarcolemmal, electron-dense plaques associated with the membrane only in those regions where vinculin was localized by immunofluorescence. Using antivinculin antibody and protein A conjugated to colloidal gold, we found that the electron-dense subsarcolemmal densities in the tonic fibers of the ALD contain vinculin; no other structures were labeled. The basal lamina overlying the densities appeared to be connected to the sarcolemma by fine, filamentous structures, more enriched at these sites than elsewhere along the muscle fiber. Increased amounts of endomysial connective tissue were often found just outside the basal lamina near the densities. In tonic ALD muscle fibers, the subsarcolemmal densities were present preferentially over the I-bands. In partially contracted ALD muscle, subsarcolemmal densities adjacent to the Z-disk appeared to be connected to that structure by short filaments. We propose that in the ALD muscle, through their association with the extracellular matrix, the densities stabilize the muscle membrane and perhaps assist in force transmission.