Analysis of the frequency and distribution of sister chromatid exchanges in cultured human lymphocytes

Summary Lymphocytes from 20 normal subjects (11 male and 9 female) were examined for the frequency and location of sister chromatid exchanges (SCE) by the BrdU—Giemsa method. The mean frequency of SCE was 6.37 with little significant variation. One subject had a high number of exchanges in chromosome 1 while the remainder showed a random distribution of exchanges between chromosomes. The frequency of exchanges generally increased with chromosome length. However, chromosome 1, 2 and the B group had more exchanges than expected while the E, F and G groups had less than expected. The distribution of exchanges in chromosomes 1, 2 and the B group was non-random with a concentration of exchanges below the centromere and to a lesser extent on the distal portion of the long arm. The majority of exchanges appeared to occur at the junction between the dark and light G bands. It is suggested that the concentration of exchanges may reflect differences in BrdU incorporation along the length of the chromosome.     

Prevalence of gallstones and gallbladder disease in Canadian Micmac Indian women.

The prevalence of gallstones and gallbladder disease was studied between October 1973 and June 1976 in Canadian Micmac Indian women aged 15 to 50 years in an inland rural community near Shubenacadie, NS. Of 132 women at risk 98 underwent cholecystography, 6 had a history of cholecystectomy (verified from hospital records) and 3 had cholecystectomy because of cholecystitis during the 3 years of the study. Of the 17 abnormal cholecystograms 10 showed radiolucent gallstones, and repeated studies documented gallstones in 6 of the 7 radiographs on which the gallbladder was not visualized. The prevalence of gallstones was found to be 211/1000, and that of gallbladder disease, 240/1000. The peak prevalence was at 30 to 39 years of age. The women with gallbladder disease were significantly more obese and of greater parity than those without gallbladder disease even when age was controlled. The Micmac Indian women of Nova Scotia appear to be at a much higher risk for the development of cholesterol gallstones and gallbladder disease than Caucasian women in Framingham, Massachusetts.     

Altered nuclear pore diameters in G1-arrested cells of the yeast Saccharomyces cerevisiae.

Nuclear pores in cells of the yeast Saccharomyces cerevisiae were examined by using the freeze-fracture technique. Nuclear pore diameters in actively growing cells appear to be exclusively of the normal diameter (75 to 115 nm), whereas some pore diameters in abnormally small G1-arrested cells produced by nitrogen starvation are unusually wide (120 to 160 nm). There may be a correlation between nuclear pore size and nuclear envelope size, the larger pores tending to occur in the smaller envelopes. The finding suggests that nuclear pore diameter may not function in regulating the flow of informational molecules from nucleus to cytoplasm, but may be implicated in regulating the flow of substrates into the nucleus.     

Mutants of yeast with depressed DNA synthesis

Summary Seven temperature-sensitive mutants have been isolated in Saccharomyces cerevisiae which show a reproducible defect in DNA synthesis at the restrictive temperature. One of these is allelic with rnal1 (Hartwell et al., 1970) but the remaining mutants define six complementation groups and probably represent six different genes. The gene symbol dds (for depressed DNA synthesis) is proposed.At the restrictive temperature, rnal1-2, dds2-1 and dds6-1 show a rapid and almost total cessation of DNA and RNA synthesis, whilst protein synthesis continues for several hours. The remaining dds mutants show a reduced rate of DNA synthesis from the time of temperature shift (dds1, dds3, dds4) or a cessation of DNA synthesis at a later time (dds5). In some cases, RNA synthesis is affected concomitantly with, or soon after, the depression in DNA synthesis. Possible reasons for the phenotypes of these mutants, and for the relative absence of yeast mutants which are unambiguously and specifically affected in DNA synthesis, are discussed.In addition, we report the isolation of seven new alleles of known cdc genes and ten new mutants with a cell cycle phenotype that complement those already known.     

A seasonal carbon budget for a laminarian population in a Scottish sea-loch

Employing in situ SCUBA methods a seasonal carbon budget has been established for aLaminaria saccharina population in a Scottish sea-loch. Concurrent studies of photosynthesis, secretion rates, reserve fluctuations and frond growth were undertaken. Net annual production is in excess of 120 g C m^–2 yr^–1. Over 13% of gross carbon input is released as extracellular secretions (over 30% in autumn) and 40–50% is lost by distal decay, entering detrital food chains. The large concentrations of laminarin, synthesised in summer months, are nearly all lost in autumn-winter distal tissue loss and therefore not available for early spring growth.     

Bombesin-induced behavioural changes: Antagonism by neuroleptics

Adult male Sprague-Dawley rats were administered bombesin (BN) intracerebroventricularly (ICV), at a dose of 0.001, 0.01, 0.1, or 1.0 μg, and the behavioural effects monitored longitudinally across time for up to 24 hr. Administration of BN significantly increased the locomotor, rearing and grooming activity at all doses. The time-course of behavioural activation was dose-related (lasting up to 2.5 hr). There was no significant difference in the behavioural response of rats receiving the BN doses in an ascending or descending order. To test the effects of dopamine receptor blockade on the BN-induced behavioural changes, groups of animals were treated with fluphenazine or haloperidol (0.1 to 2.5 mg/kg, IP) 30 min prior to BN (1 μg, ICV) administration. The results revealed that the neuroleptics could effectively antagonize the BN-induced activation of locomotor, rearing and grooming activity. These data are concordant with the view that centrally administered BN stimulates spontaneous exploratory and grooming behaviours in rats, in a time- and dose-related manner. Furthermore, since neuroleptics block these effects, it remains possible that the BN-induced behavioural changes may be mediated, at least in part, through the dopaminergic system(s).     

On the mechanism of premeiotic DNA synthesis in the yeast Saccharomyces cerevisiae

Premeiotic DNA synthesis in synchronously sporulating cultures of the yeast, Saccharomyces cerevisiae, was analysed by sedimentation in alkaline sucrose gradients and by DNA-fibre autoradiography. The gradient profiles of cells pulse-labelled for varying times were essentially identical with those obtained with mitotic cultures, revealing a close resemblance between the meiotic and mitotic replication mechanisms. This was supported by the finding that exposure of meiotic cells to a specific concentration of hydroxyurea led to the accumulation of completed, but unjoined replicons, just as it does in mitotic cells. The results of DNA-fibre autoradiography confirmed that replicons in meiotic cells are the same size (20–180 Kb, averaging around 90 Kb) as in mitotic cells, and assuming replication is bi-directional, replication forks must move at round the same rate as in mitosis, i.e. about 0.7 μm/min.     

Association of Rab3A with synaptic vesicles at late stages of the secretory pathway

Rab3A is a small GTP-binding protein highly concentrated on synaptic vesicles. Like other small GTP-binding proteins it is thought to cycle between a soluble and a membrane-associated state. To determine at which stage of the life cycle of synaptic vesicles rab3A is associated with their membranes, the localization of the protein in neurons and neuroendocrine cells at different developmental and functional stages was investigated. In all cases, rab3A was colocalized with synaptic vesicle markers at the cell periphery, but was absent from the Golgi area, suggesting that rab3A associates with vesicles distally to the Golgi complex and dissociates from vesicle membranes before they recycle to this region. Immunofluorescence experiments carried out on frog motor end plates demonstrated that massive exocytosis of synaptic vesicles is accompanied by a translocation of rab3A to the cell surface. The selective localization of rab3A on synaptic vesicles at stages preceding their fusion with the plasmalemma suggests that the protein is part of a regulatory machinery that is assembled onto the vesicles in preparation for exocytosis.     

The amino acid sequence of peanut agglutinin

The amino acid sequence of peanut (Arachis hypogaea) agglutinin was determined from three major fragments obtained by mild acid cleavage at Asp-Pro peptide bonds. The sequence of 236 amino acids has residues identical to those that form the metal-binding site and the hydrophobic pocket in concanavalin A and other lectins, although the overall similarity is only 42%. In the segments of peanut agglutinin that correspond to the four loops that form the carbohydrate-binding site in concanavalin A and favin, several central residues are homologous, while others show changes to smaller side chains, such as Tyr----Gly. The carbohydrate-binding site of peanut agglutinin may therefore have a similar peptide-backbone architecture, but form a considerably more open cleft.