The rabbit alpha-like globin gene cluster is polymorphic both in the sizes of BamHI fragments and in the numbers of duplicated sets of genes

The alpha-like globin gene cluster in rabbits contains embryonic zeta- globin genes, an adult alpha-globin gene, and theta-globin genes of undetermined function. The basic arrangement of genes, deduced from analysis of cloned DNA fragments, is 5'-zeta 0-zeta 1-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3'. However, the pattern of restriction fragments containing zeta- and theta-globin genes varies among individual rabbits. Analysis of BamHI fragments of genomic DNA from 24 New Zealand white rabbits revealed eight different patterns of fragments containing zeta-globin genes. The large BamHI fragments containing genes zeta 0 and zeta 1 are polymorphic in length, whereas a 1.9-kb fragment containing the zeta 2 gene and the 3.5-kb fragment containing the zeta 3 gene do not vary in size. In contrast to this constancy in the size of the restriction fragments, the copy number of the zeta 2 and zeta 3 genes does vary among different rabbits. No length polymorphism was detected in the BamHI fragments containing the theta-globin genes, but again the copy number varies for restriction fragments containing the theta 2 gene. The alpha 1- and theta 1-globin genes are located in a nonpolymorphic 7.2-kb BamHI fragment. The combined data from hybridization with both zeta and theta probes shows that the BamHI cleavage pattern does not vary within the region 5'-alpha 1-theta 1- zeta 2-zeta 3-theta 2-3', but the pattern genomic blot-hybridization patterns for the progeny of parental rabbits with different zeta-globin gene patterns shows that the polymorphic patterns are inherited in a Mendelian fashion. Two different haplotypes have been mapped based on the genomic blot-hybridization data. The variation in the alpha-like globin gene cluster in the rabbit population results both from differences in the copy number of the duplication block containing the zeta-zeta-theta gene set and from the presence or absence of polymorphic BamHI sites.      

Evidence for a role of protein kinase C zeta subspecies in maturation of Xenopus laevis oocytes.

A number of studies have demonstrated the activation of phospholipase C-mediated hydrolysis of phosphatidylcholine (PC-PLC) both by growth factors and by the product of the ras oncogene, p21ras. Evidence has been presented indicating that the stimulation of this phospholipid degradative pathway is sufficient to activate mitogenesis in fibroblasts as well as that it is sufficient and necessary for induction of maturation in Xenopus laevis oocytes. However, the mechanism whereby PC-PLC transduces mitogenic signals triggered by growth factors or oncogenes remains to be elucidated. In this study, data are presented that show the involvement of protein kinase C zeta subspecies in the channelling of the mitogenic signal activated by insulin-p21ras-PC-PLC in Xenopus oocytes as well as the lack of a critical role of protein kinase C isotypes alpha, beta, gamma, delta, and epsilon in these pathways.     

Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

Plasmid pSC101 harbors a recombination site, psi, which is able to resolve plasmid multimers and to substitute for the analogous chromosomal Escherichia coli site dif.

Plasmid pSC101 harbors a 28-bp sequence which is homologous to dif, the target site of the XerC/XerD-dependent recombination system in Escherichia coli. Using a technique which allows very sensitive detection of plasmid loss, we show that recombination at this site, termed psi for pSC101 stabilized inheritance, causes a moderate increase in pSC101 stability. The role of the psi sequence in site-specific recombination has been explored in two other contexts. It was cloned in a derivative of plasmid p15A and inserted into the chromosome in place of dif. In the first situation, psi activity requires accessory sequences and results in multimer resolution; in the second situation, it suppresses the effects of the dif deletion and can promote intermolecular exchanges. Thus, psi is a site whose recombinational activity depends on the context, the first in the cer/dif family known to exhibit such flexibility.     

Unraveling a Region-Specific Hyper-Recombination Phenomenon: Genetic Control and Modalities of Terminal Recombination in Escherichia Coli

The propensity of the terminus of the Escherichia coli chromosome for recombination has been further explored, using a test based on the selectable loss of a λ prophage inserted between repeated sequences from Tn10. Terminal recombination appears region-specific and unrelated to replication termination in a strain harboring a major chromosomal rearrangement. It requires RecBC(D) activity and must therefore occur between sister chromosomes, to conserve genomic integrity in spite of DNA degradation by RecBCD. Terminal recombination is maximal in the dif region and its intensity on either side of this recombination site depends on the orientation of the repeated sequences, probably because of the single χ site present in each repeat. Additional observations support the model that the crossover is initiated by single-strand invasion between sister chromosomes followed by RecBCD action as a consequence of DNA breakage due to the initial invasion event. Crossover location within repeats inserted at dif position supports the possibility that sister chromosomes are tightly paired in the centre of the terminal recombination zone. These data reinforce the model that postreplicative reconstruction of nucleoid organization creates a localized synapsis between the termini of sister chromosomes.     

The cause of slow increase of heart rate during muscular exercise in man]

The slow increase in heart rate which is observed in normal man submitted to heavy muscular exercise is due for a part to an activation of orthosympathetic cardiac activity which is blocked by beta antagonists. It is also explained by direct action of hyperthermia on the heart.     

Modulation of interleukin 2 internalization and interleukin 2-dependent cell growth by antireceptor antibodies

The growth factor interleukin 2 (IL2) binds to and is internalized together with high-affinity surface receptors present on lymphoid cells. This endocytosis thus results in down-regulation of the receptors. However, it is not known if the internalization is relevant to the induction of cell growth. In the present study a rat monoclonal antibody to the P55 chain of the IL2 receptor was used to examine the role of receptor internalization in the IL2-dependent autocrine human tumor T cell line IARC 301. When given alone, this antibody did not inhibit IL2 binding, internalization, or IL2-dependent cell proliferation. However, crosslinking by anti-rat immunoglobulins, which did not affect binding of the growth factor, inhibited both IL2 internalization and cell proliferation. Besides offering a novel means for the specific inhibition of the uptake of IL2 bound to IL2 high-affinity receptors, the results are compatible with the association of this receptor-ligand uptake to the growth stimulation by IL2.     

Mechanism of inhibition of adenylate cyclase by phospholipase C-catalyzed hydrolysis of phosphatidylcholine. Involvement of a pertussis toxin-sensitive G protein and protein kinase C.

The phospholipase C-mediated hydrolysis of phosphatidylcholine has been shown recently to be activated by a number of agonists. Muscarinic receptors, which trigger various signal transduction mechanisms including inhibition of adenylate cyclase through Gi, have been shown to be potent stimulants of this novel phospholipid degradative pathway. We demonstrate here, by exogenous addition of Bacillus cereus phosphatidylcholine-hydrolyzing phospholipase C, that phosphatidylcholine breakdown mimics the ability of carbachol to inhibit adenylate cyclase. This effect is sensitive to pertussis toxin and is entirely dependent on the presence of protein kinase C. This kinase is also required for the inhibition by carbachol of adenylate cyclase. These results suggest that the activation of phosphatidylcholine breakdown by phospholipase C may play an important role linking or favoring the coupling muscarinic receptors to Gi. Results presented here also show that phospholipase C-mediated hydrolysis of phosphoinositides by exogenous addition of Bacillus thuringiensis phosphoinositide-hydrolyzing phospholipase C does not affect adenylate cyclase, despite the fact that protein kinase C is translocated to an extent similar to that produced by the hydrolysis of phosphatidylcholine. According to the results shown here, both phospholipases also differ in their ability to down-regulate protein kinase C as well as to phosphorylate p80 and to transmodulate the binding of epidermal growth factor, two well established effects of protein kinase C in Swiss 3T3 fibroblasts. This emphasizes the complexity, from a functional point of view, of protein kinase C activation "in vivo."