Crosslinking of phycobiliproteins from the cyanobacterium Mastigocladus laminosus with bis-imidates: localization of an intrasubunit and an intersubunit crosslink in C-phycocyanin

The light-harvesting pigment-protein complexes allophycocyanin (AP), C-phycocyanin (PC) and phycoerythrocyanin (PEC) of the cyanobacterium Mastigocladus laminosus consist of alpha- and beta-subunits containing about 170 amino-acid residues each. These two subunits form an alpha,beta-monomer, three of which build up a disc-shaped trimer. In this study these phycobiliproteins were crosslinked with bis-imidates. Various spacer lengths of the reagent and various aggregation states of the phycobiliprotein were tested. An intersubunit crosslink could be verified in all three phycobiliproteins. PC-trimers were crosslinked with the homobifunctional reagent dimethyl pimelimidate having a maximal crosslinking distance of 10 A. Two crosslinks could be identified: an intramonomer intersubunit crosslink with a yield of 48% and an intrasubunit crosslink within alpha PC (57%). These products were chemically and enzymatically fragmented and the small crosslinked peptides were isolated and then identified by amino-acid analysis. The following amino acids were crosslinked: alpha-Val 1 with beta-Ala 1 and alpha-Lys 62 with alpha-Lys 134. Both crosslinks could be localized within the known three-dimensional structure of PC.     

Forces in the spider orb web

Summary Pretensile forces were measured in individual threads of intact spider webs. In the orb web of Araneus diadematus forces decrease from mooring threads to frame threads and radii, a typical ratio being 1071. The smaller number of radii in the upper than in the lower half of the orb is paralleled by force ratios of 21 to 31. A similar difference between radii built first during web construction and radii added after completion of the frame underlines the importance of the former as part of the scaffolding. High tensions in the auxiliary spiral stabilize the radii in addition to providing a pathway for the spider when inserting the sticky spiral. Radial pretension (F) changes with spider mass (m). F/m is similar for different animals indicating an adaptation of radial forces to those resulting from spider mass. Several observations suggest tension control by the spider. When forced to anchor its web to thin flexible rods tension in the threads remains in the normal range. Tension values are similar in the webs of A. diadematus, Zygiella x-notata, Nuctenea umbratica, and Nephila clavipes indicating independence from details of web geometry. Only the mooring threads of Nephila show unusually large forces suggesting a narrower working range of tensions for the catching area than for the scaffolding.     

The gene for autosomal dominant polycystic kidney disease lies in a 750-kb CpG-rich region.

PKD1, the locus most commonly affected by mutations that produce autosomal dominant polycystic kidney disease (ADPKD), has previously been localized to chromosome 16p13.3. Since no cytogenetic abnormalities have been found in association with ADPKD, flanking genetic markers have been required to define an interval--the PKD1 region--that contains the PKD1 gene. In this report we demonstrate, through the construction of a long-range restriction map that links the flanking genetic markers GGG1 (D16S84) and 26.6PROX (D16S125), that the PKD1 gene lies within an extremely CpG-rich 750-kb segment of chromosome 16p13.3. Approximately 90% of this region has been cloned in three extensive cosmid/bacteriophage contigs. The cloned DNA is a valuable resource for identifying new closer flanking genetic markers and for isolating candidate genes from the region.     

Transformation of bacteria with plasmid DNA by electroporation

The possibility of electric field-mediated transformation ("electroporation") of a gram-positive bacterium (Enterococcus faecalis) and two gram-negative bacteria (Escherichia coli and Pseudomonas putida) with plasmid DNA was investigated. E. faecalis protoplasts could be transformed by electroporation with a transformation frequency of 10(4) to 10(5) transformants/micrograms plasmid. Untreated--i.e., washed--cells of E. coli could be transformed with rates of 1 X 10(5) transformants/micrograms plasmid DNA. Transformation rates for P. putida cells were up to 3 X 10(4) if the method developed for E. coli was used. Detailed protocols for these systems, including the results of various optimization experiments, are given.     

Structure and genomic organization of a new family of murine retrovirus-related DNA sequences (MuRRS).

A new class of murine retrovirus-related sequences (MuRRS) is described. These 5.7 kb long transposon-like DNA-elements start and end with approximately 600 bp long repeats identical to previously identified solitary LTR-like elements (LTR-IS). There are about 50 - 100 5.7 kb elements and about 500 - 1000 solo LTR-IS elements per mouse haploid genome. Sequence analysis of one cloned MuRRS element revealed several possible open reading frames with partial sequence homologies to retroviral gag, pol and env genes.     

Macrophage mediation of the inhibitory effects of elevated intracellular levels of adenosine-3':5' cyclic monophosphate (cAMP) on macrophage-Trypanosoma cruzi association

Presence of theophylline and dibutyryl-cAMP—agents which cause elevation of intracellular levels of cAMP—in in vitro systems in which murine macrophages interact with virulent blood forms of Trypanosoma cruzi resulted in a marked inhibition of cell-parasite association (i.e., decreased surface binding and/or internalization). This effect was evidenced in terms of significant reductions in both the percentage of infected macrophages and the average number of trypanosomes per 100 macrophages. Pretreatment of the macrophages with these agents produced a similar inhibition whereas pretreatment of the parasites had no significant consequence on the interaction. The inhibitory effect was transient since it was no longer seen after 30 min of incubation of the treated macrophages in fresh medium. Thus, the inhibitory effect is exerted through a transient effect on the macrophage.     

Acridine-psoralen amines and their interaction with deoxyribonucleic acid

A series of novel compounds in which a 9-acridinyl nucleus is linked to a psoralen nucleus in the 5- or 8-position via polyamines was prepared and examined. Their reversible binding to DNA and their irreversible binding to DNA and DNA cross-linking upon irradiation with UV-A light were examined. It was found that they were all less efficiently photoreactive than 8-methoxypsoralen (8-MOP), both in cross-linking and photobinding to DNA, whereas the ratio between their photobinding and cross-linking was 40-400 times that of 8-MOP. Compounds in which the linker was attached to the 5-position in psoralen showed smaller cross-linking and photobinding efficiencies and larger ratios between photobinding and cross-linking than those of psoralens attached in the 8-position. This strongly indicates that the 9-substituents of the acridines are oriented toward the minor groove. Flow linear dichroism studies showed that the compounds were DNA intercalating with the acridine moiety, whereas the psoralen moiety in no case was clearly intercalating. This conclusion was further supported by viscometry which also strongly indicated monointercalation.