The cloning of chromosomal DNA associated with methicillin and other resistances in Staphylococcus aureus

Competitive hybridization was used to detect the deletion of chromosomal DNA accompanying the loss of resistance to methicillin (and concomitantly, to cadmium, mercury and tetracycline) from a clinical strain of methicillin-resistant Staphylococcus aureus (MRSA). The method was also used to screen a partial plasmid library of chromosomal HindIII fragments from the MRSA strain. Eight recombinant plasmid clones were identified as containing DNA included in the deletion. These clones were used as probes to screen a phage library of the total DNA of the same MRSA strain, resulting in the isolation of overlapping recombinant phage clones carrying 24 kb of the deleted DNA. Two of the cloned HindIII fragments were associated closely with methicillin resistance, as shown by probing DNA from an independent methicillin-sensitive/resistant transduced strain pair and from two MRSA strains following growth in the presence of high concentrations of methicillin. The endonuclease map of the cloned DNA indicates the presence of four copies of a direct repeat less than 1 kb in size. The map is also consistent with the presence in the chromosome of sequences for mercury resistance (mer A mer B) and for tetracycline-resistance plasmid pT181.     

Effects of sulphuric acid exposure on the behaviour of largemouth bass,Micropterus salmoides

Synopsis Young-of-the-year largemouth bass,Micropterus salmoides, were exposed to four concentrations of sulphuric acid (pH levels 7.2, 6.1, 4.8, and 3.7) for 30 days, and the frequencies of feeding acts and activity bouts, and time budgets were recorded. Juveniles at pH 6.1 and at pH 4.8 performed the two feeding acts, bites and orientations, more often, and spent more time feeding than bass at pH 7.2. Bass at pH 3.7, however, reduced feeding, and spent a significantly larger portion of their time hovering in the water column. Frequencies of comfort and agonistic acts increased with a decline in pH. Alterations of behavioural repertoires of young-of-the-year largemouth bass were useful indicators of sulphuric acid exposure.     

Serum lipids and lipoproteins in the atherosclerosis prone LA/N corpulent rat

The LA/N rat is one of two congenic strains bred from the original obese, hyperphagic and hypertensive rats of Koletsky. With the exception of hypertension the LA/N strain, when homozygous for the corpulent gene, is phenotypically similar to the parent Koletsky strain and prone to the development of vascular and myocardial lesions. Here we report a detailed analysis of the serum lipids, lipoproteins and apolipoproteins B, E and A-I levels in young adult homozygous corpulent (cp/cp) rats of both sexes and in lean males of the same age which were demonstrable non-carriers (+/+) of the cp gene. Both male and female cp/cp rats were hypertriglyceridemic (282-512 mg/100 ml) and moderately hypercholesterolemic (74-84 mg/100 ml). Elevations in these lipids reflected the presence of large (622 A), triacylglycerol-rich and apoprotein-poor VLDL containing both apolipoproteins Bh and B1 and increased phospholipid-rich HDL. Similar, but less pronounced, elevations in serum apolipoproteins B and E in the cp/cp rats when compared to the +/+ animals were also noted. Apolipoproteins A-I levels were 2.7-3-fold higher in cp/cp rats. The levels of VLDL were significantly higher in female cp/cp rats; however, the levels of IDL (intermediate-density lipoproteins), LDL and HDL were significantly lower than in the more atherosclerosis prone male cp/cp rats. Similarly, apolipoprotein A-I was higher and apolipoprotein B lower in the male cp/cp than in the female cp/cp rats. The LDL (d = 1.030-1.063 g/ml) in cp/cp rats, like that in normal animals, was heterogeneous and contained apolipoproteins Bh, E, A-I and C. This fraction was significantly elevated in male cp/cp rats when compared to females but still represented less than 13% of the total serum cholesterol and less than 6% of the total serum lipids in 3-month-old cp/cp animals. The ratio of cholesterol to phospholipids was significantly lower for all lipoproteins in cp/cp rats when compared to +/+ males and these ratios for female cp/cp rats were in all cases lower than those of male cp/cp animals.     

Determination of the source of immunoreactive relaxin in the cat

We have recently reported the secretory profile of relaxin throughout gestation in the cat. Because the appearance of relaxin begins at about Day 20 (Day O = ovulation) and because implantation begins shortly before this at Days 13-14, we hypothesized that relaxin was of feto-placental origin. To test this hypothesis, we used 4 experimental groups: 1) Control (laparotomy-only at Day 23 or 42, n = 4); 2) Early Ovariectomy (Ovx, bilateral ovariectomy between Days 23 and 26, n = 4); 3) Late Ovx (bilateral ovariectomy between Days 40 and 44, n = 4); 4) Tissue Removal (removal of feto-placental units, uterus, and one ovary on Days 16, 21, 28 and 35, n = 1 per day). Pregnancies were maintained in both Ovx groups by progesterone administration. Relaxin secretory patterns in Ovx groups were similar to the Control data. Relaxin was detectable in plasma beginning at about Day 20, with maximum concentrations reached by Day 30. Relaxin concentrations were highest (immunoactivity per mg tissue) in homogenates of placental tissues as compared to luteal, fetal, or uterine tissues. Altogether, these data indicate that the feto-placental unit is the source of relaxin in the cat.     

The Putative Oncogene Pim-1 in the Mouse: Its Linkage and Variation among t Haplotypes

Pim-1, a putative oncogene involved in T-cell lymphomagenesis, was mapped between the pseudo-alpha globin gene Hba-4ps and the alpha-crystallin gene Crya-1 on mouse chromosome 17 and therefore within the t complex. Pim-1 restriction fragment variants were identified among t haplotypes. Analysis of restriction fragment sizes obtained with 12 endonucleases demonstrated that the Pim-1 genes in some t haplotypes were indistinguishable from the sizes for the Pim-1b allele in BALB/c inbred mice. There are now three genes, Pim-1, Crya-1 and H-2 I-E, that vary among independently derived t haplotypes and that have indistinguishable alleles in t haplotypes and inbred strains. These genes are closely linked within the distal inversion of the t complex. Because it is unlikely that these variants arose independently in t haplotypes and their wild-type homologues, we propose that an exchange of chromosomal segments, probably through double crossingover, was responsible for indistinguishable Pim-1 genes shared by certain t haplotypes and their wild-type homologues. There was, however, no apparent association between variant alleles of these three genes among t haplotypes as would be expected if a single exchange introduced these alleles into t haplotypes. If these variant alleles can be shown to be identical to the wild-type allele, then lack of association suggests that multiple exchanges have occurred during the evolution of the t complex.     

Variation in Male Fertilities and Pairwise Mating Probabilities in Picea glauca

Frequencies of multilocus male gametes in seeds collected from clones in several blocks of a white spruce seed orchard were analyzed as part of a 2-yr study of mating system variation in this species. Observed frequencies of male gamete types departed significantly from those expected assuming equal male fertilities among clones. Male gamete frequencies in seed crops were significantly heterogeneous among clones within blocks, and among blocks within clones. Clonal male fertilities were estimated from male gamete frequency data. These estimates were highly skewed, with a small proportion of the clones contributing male gametes to the majority of the seed. The estimates were significantly heterogeneous among clones within blocks, and among blocks within clones. Between-year variation in clonal male fertilities was also pronounced, with male fertilities of some clones changing by as much as three orders of magnitude. Clonal male fertility was significantly correlated with clonal male cone production in both years. These results are important with regard to assumptions made for the estimation of general combining ability, average genetic correlation among progeny from single parents, and expected response to selection in open-pollinated plant populations.     

Gene sequence for the 9 kDa component of Photosystem II from the cyanobacterium Phormidium laminosum indicates similarities between cyanobacterial and other leader sequences

Summary A 9 kDa polypeptide which is loosely attached to the inner surface of the thylakoid membrane and is important for the oxygen-evolving activity of Photosystem II in the thermophilic cyanobacterium Phormidium laminosum has been purified, a partial amino acid sequence obtained and its gene cloned and sequenced. The derived amino acid sequence indicates that the 9 kDa polypeptide is initially synthesised with an N-terminal leader sequence of 44 amino acids to direct it across the thylakoid membrane. The leader sequence consists of a positively charged N-terminal region, a long hydrophobic region and a typical cleavage site. These features have analogous counterparts in the thylakoid-transfer domain of lumenal polypeptides from chloroplasts of higher plants. These findings support the view of the proposed function of this domain in the two-stage processing model for import of lumenal, nuclear-encoded polypeptides. In addition, there is striking primary sequence homology between the leader sequences of the 9 kDa polypeptide and those of alkaline phosphatase (from the periplasmic space of Escherichia coli) and, particularly in the region of the cleavage site, the 16 kDa polypeptide of the oxygen-evolving apparatus in the thylakoid lumen of spinach chloroplasts.     

Fermentation of barley straw by anaerobic rumen bacteria and fungi in axenic culture and in co-culture with methanogens

When incubated in axenic culture, strains of anaerobic rumen fungi were more active than cellulolytic bacteria in solubilizing barley straw stem fragments 5 to 10 mm in length. Pretreatment with ammonia had little effect on microbial attack. Of three species of methanogens tested, Methanobrevibacter smithii strain PS formed the most stable and reproducible co-cultures with the fungi and with Ruminococcus albus , and the presence of this organism enhanced the extent of degradation of straw, although this effect was less marked than that previously observed when pure cellulose was used as substrate.