Early events in the replication of Mu prophage DNA.

To determine whether the early replication of Mu prophage DNA proceeds beyond the termini of the prophage into hose DNA, the amounts of both Mu DNA and the prophage-adjacent host DNA sequences were measured using a DNA-DNA annealing assay after induction of the Mu vegetative cycle. Whereas Mu-specific DNA synthesis began 6 to 8 min after induction, no amplification of the adjacent DNA sequences was observed. These data suggest that early Mu-induced DNA synthesis is constrained within the boundaries of the Mu prophage. Since prophage Mu DNA does not undergo a prophage lambda-like excision from its original site after induction (E. Ljungquist and A. I. Bukhari, Proc. Natl. Acad. Sci. U.S.A. 74:3143--3147, 1977), we propose the existence of a control mechanism which excludes prophage-adjacent sequences from the initial mu prophage replication. The frequencies of the Mu prophage-adjacent DNA sequences, relative to other Escherichia coli genes, were not observed to change after the onset of Mu-specific DNA replication. This suggests that these regions remain associated with the host chromosome and continue to be replicated by the chromosomal replication fork. Therefore, we conclude that both the Mu prophage and adjacent host sequences are maintained in the host chromosome, rather than on an extrachromosomal form containing Mu and host DNA.     

Kinetic analyses demonstrate that the equilibrium assumption does not apply to [125I]endothelin-1 binding data.

The kinetics of [125I]Endothelin-1 ([125I]ET-1) binding were studied using membranes from rat heart, rat lung, rat brain, and porcine vascular smooth muscle at 37 degrees C in 0.05M Tris-HCl buffer (pH = 7.4). The dissociation half-life (t1/2, diss.) for bound [125I]ET-1 was in excess of 30 hours for each tissue studied. Equilibrium-time requirements for proper Scatchard analysis of [125I]ET-1 were also far in excess of 30 hours for each tissue. These data suggest that determination of dissociation constants, Kd, and receptor concentrations, Bmax, by conventional Scatchard analysis is not feasible with [125I]ET-1. Kinetic analyses may provide a more accurate means for determining [125I-ET-1] binding characteristics including Kd and Bmax.     

Improvements in optical methods for measuring rapid changes in membrane potential

Summary In an effort to increase the utility of optical methods for measuring membrane potential in excitable cells, an additional 369 dyes were tested on giant axons from the squid. Several promising dyes with relatively large absorption and fluorescence signals are described. In addition, a simple modification of the apparatus led to a sixfold increase in the size of dye-related birefringence signals. In preparations with a suitable geometry, these signals are as large as absorption signals but photodynamic damage and bleaching are eliminated when wavelengths longer than the absorption band are used.     

Cellular location of Mu DNA replicas.

To ascertain the form and cellular location of the copies of bacteriophage Mu DNA synthesized during lytic development, DNA from an Escherichia coli lysogen was isolated at intervals after induction of the Mu prophage. Host chromosomes were isolated as intact, folded nucleoids, which could be digested with ribonuclease or heated in the presence of sodium dodecyl sulfate to yield intact, unfolded nucleoid DNA. Almost all of the Mu DNA in induced cells was associated with the nucleoids until shortly before cell lysis, even after unfolding of the nucleoid structure. We suggest that the replicas of Mu DNA are integrated into the host chromosomes, possibly by concerted replication-integration events, and are accumulated there until packaged shortly before cell lysis. Nucleoids also were isolated from induced lambda lysogens and from cells containing plasmid DNA. Most of the plasmid DNA sedimented independently of the unfolded nucleoid DNA, whereas 50% or more of the lambda DNA from induced lysogens cosedimented with unfolded nucleoid DNA. Possible explanations for the association of extrachromosomal DNA with nucleoid DNA are discussed.     

Water uptake and water diffusivity of seeds

When pea (Pisum sativum) seeds were wetted, a sharp front separated the wet and dry portions, the seeds swelled, and the water content in the wetted portion continued to increase for a long time. A model was proposed and tested that takes into account these three characteristics and in particular does not postulate a constant diffusivity. The parameters of the model are simply the rate of penetration of the wetting front and a swelling factor.     

Armenian hamster female protein (serum amyloid P component). Comparison with the sex-regulated homolog in Syrian hamster

Complementary DNA clones for Armenian hamster female protein (FP) were isolated and the complete nucleotide sequence and derived amino acid sequence were determined and compared with relevant data for the closely related Syrian hamster. Although biosynthesis of preSAP is directed by a 1.0-kb mRNA in both genera and the molecular mass of the primary translation product of FP is identical, the FP gene structure and regulation of expression of FP are different in Syrian and Armenian hamsters. Whereas the direction of alteration in FP mRNA levels is divergent in Syrian hamsters during an acute phase reaction, hepatic FP mRNA levels increase in both male and female Armenian hamsters during inflammation. Regulation of expression of Armenian and Syrian hamster FP genes occurs at a pretranslational level.     

Biodeterioration of Mayan buildings at uxmal and tulum,Mexico

Uxmal and Tulum are two important Mayan sites in the Yucatan peninsula. The buildings are mainly composed of limestone and grey/black discoloration is seen on exposed walls and copious greenish biofilms on inner walls. The principal microorganisms detected on interior walls at both Uxmal and Tulum were cyanobacteria; heterotrophic bacteria and filamentous fungi were also present. A dark‐pigmented mitosporic fungus and Bacillus cereus, both isolated from Uxmal, were shown to be acidogenic in laboratory cultures. Cyanobacteria belonging to rock‐degrading genera Synechocystis and Gloeocapsa were identified at both sites. Surface analysis previously showed that calcium ions were present in the biofilms on buildings at Uxmal and Tulum, suggesting the deposition of biosolubilized stone. Apart from their potential to degrade the substrate, the coccoid cyanobacteria supply organic nutrients for bacteria and fungi, which can produce organic acids, further increasing stone degradation.