Composition and molecular weight of pili purified from Pseudomonas aeruginosa K.

Pseudomonas aeruginosa strain K (PAK) bears polar pili that promote infection by at least six bacteriophages. Moreover, a recently isolated mutant of strain K (PAK/2PfS) is many times more piliated than the wild-type strain and facilitates the preparation of large amounts of pure pili for biochemical studies. The present investigation was carried out to establish the structural relatedness of PAK and PAK/2PfS pili and to determine their biochemical composition. A purfication procedure is described for PAK and PAK/2PfS pili that yields about 8 mg of pure pili per 100 g (wet weight) of PAK/2PfS cells and 0.8 mg of pure pili per 100 g (wet weight) of PAK cells. PAK and PAK/2PfS pili were found to be free from phosphate, carbohydrate, and lipid and to contain a single polypeptide subunit of 17,800 daltons. Isopycnic centrifugation studies revealed that PAK and PAK(2PfS pili have the same buoyant density in sucrose (1.221) and CsC1 (1.295). Both types of pili banded at pH 3.9 when subjected to isoelectric focusing. Amino acid analyses showed that PAK and PAK/2PfS pili have identical amino acid compositions, whereas microimmunodiffusion studies revealed that the two types of pili are immunologically indistinguishable. It was concluded that PAK and PAK/2PfS pili are identical and that the mutation responsible for producing the multipiliated state in PAK/2PfS is probably located outside the structural gene for PAK pili.     

The Tra2 core of the IncP(alpha) plasmid RP4 is required for intergeneric mating between Escherichia coli and Streptomyces lividans.

Escherichia coli cells and Streptomyces mycelia are able to form close contacts in the absence of a conjugative system which might facilitate intergeneric plasmid transfer without the genes required for mating pair formation (Tra2) of the RP4 plasmid. The same Tra2 genes found to be essential for RP4 plasmid transfer, RSF1010 mobilization, and donor-specific phage propagation in E. coli were also required for intergeneric transfer between E. coli and Streptomyces lividans.     

Worldwide patterns of mitochondrial DNA differentiation in the harbor seal (Phoca vitulina)

The harbor seal (Phoca vitulina) has one of the broadest geographic distributions of any pinniped, stretching from the east Baltic, west across the Atlantic and Pacific Oceans to southern Japan. Although individuals may travel several hundred kilometers on annual feeding migrations, harbor seals are generally believed to be philopatric, returning to the same areas each year to breed. Consequently, seals from different areas are likely to be genetically differentiated, with levels of genetic divergence increasing with distance. Differentiation may also be caused by long-standing topographic barriers such as the polar sea ice. We analyzed samples of 227 harbor seals from 24 localities and defined 34 genotypes based on 435 bp of control region sequence. Phylogenetic analysis and analysis of molecular variance showed that populations in the Atlantic and Pacific Oceans and east and west coast populations of these oceans are significantly differentiated. Within these four regions, populations that are geographically farthest apart generally are the most differentiated and often do not share genotypes or differ in genotype frequency. The average corrected sequence divergence between populations in the Atlantic and Pacific Oceans is 3.28% +/- 0.38% and those among populations within each of these oceans are 0.75% +/- 0.69% and 1.19% +/- 0.65%, respectively. Our results suggest that harbor seals are regionally philopatric, on the scale of several hundred kilometers. However, genetic discontinuities may exist, even between neighboring populations such as those on the Scottish and east English coasts or the east and west Baltic. The mitochondrial data are consistent with an ancient isolation of populations in both oceans, due to the development of polar sea ice. In the Atlantic and Pacific, populations appear to have been colonized from west to east with the European populations showing the most recent common ancestry. We suggest the recent ancestry of European seal populations may reflect recolonization from Ice Age refugia after the last glaciation.      

Analysis of the sequence and gene products of the transfer region of the F sex factor.

Bacterial conjugation results in the transfer of DNA of either plasmid or chromosomal origin between microorganisms. Transfer begins at a defined point in the DNA sequence, usually called the origin of transfer (oriT). The capacity of conjugative DNA transfer is a property of self-transmissible plasmids and conjugative transposons, which will mobilize other plasmids and DNA sequences that include a compatible oriT locus. This review will concentrate on the genes required for bacterial conjugation that are encoded within the transfer region (or regions) of conjugative plasmids. One of the best-defined conjugation systems is that of the F plasmid, which has been the paradigm for conjugation systems since it was discovered nearly 50 years ago. The F transfer region (over 33 kb) contains about 40 genes, arranged contiguously. These are involved in the synthesis of pili, extracellular filaments which establish contact between donor and recipient cells; mating-pair stabilization; prevention of mating between similar donor cells in a process termed surface exclusions; DNA nicking and transfer during conjugation; and the regulation of expression of these functions. This review is a compendium of the products and other features found in the F transfer region as well as a discussion of their role in conjugation. While the genetics of F transfer have been described extensively, the mechanism of conjugation has proved elusive, in large part because of the low levels of expression of the pilus and the numerous envelope components essential for F plasmid transfer. The advent of molecular genetic techniques has, however, resulted in considerable recent progress. This summary of the known properties of the F transfer region is provided in the hope that it will form a useful basis for future comparison with other conjugation systems.     

Binocular responses of neurons in the barn owl's visual Wulst

Binocular responses have been recorded extra-cellularly at 58 sites in the barn owl's (Tyto alba) visual Wulst. Neurons showed disparity tuning to stimulation with moving bars, moving sinewave gratings and a moving visual-noise stimulus. Responses to sinewave gratings as a function of disparity were cyclic, with the period of a cycle of the response being correlated to one cycle of the stimulus. Cyclic responses were also found when bars or noise were used as a stimulus, but, especially in response to visual noise, one response peak, the main peak, was different from the other peaks, the sidepeaks: usually, the main peak was either higher or narrower or both higher and narrower than the sidepeaks. When the responses to different spatial frequencies were compared, response maxima coincided at the main peak, but not at the other peaks. In analogy to auditory physiology the disparity at which the frequency-independent peak occurs is termed characteristic disparity. Spatial-frequency tuning revealed broad tuning, ranging from 1 to more than 3 octaves at 50% of the maximal response. Disparity tuning was broad at the onset of the response and sharpened later. The data are discussed within the framework of a model for the neural representation of visual disparity that was derived from a model proposed earlier for the representation of interaural time difference, the main cue for encoding sound-source azimuths in the barn owl.Abbreviations ITD interaural time difference - CD characteristic delay - RF receptive field     

Staining of fresh, Undecalcified, thin Bone Sections

Fresh, undecalcified bone sections can be reproducibly and reliably stained by any of the following procedures: (A) Basic fuchsin, 1% in 30% alcohol, 48 hr, 22°C. (B) AgNO₃, 0.033 M, 48 hr, 22°C; washing 48 hr in a large volume of distilled water; exposure to light to develop the color. (C) Metallic sulfides (Co⁺⁺, Pb⁺⁺, Hg⁺⁺, Cu⁺⁺): the nitrate of the metal, 0.033 M, 48 hr, 22°C; then Na₂S, 0.033 M, 48 hr, 22° C. (D) Alizarin Red S, 0.1% solution in distilled water, 48 hr, 22°C; differentiated 48 hr at 22°C in weakly alkaline water, pH about 8. (E) KMnO₄: boiling 8-10 min in a 0.1 N, solution. With the exception of D the surface stain must be ground off the section for microscopic examination of its interior. Stain concentration, time and temperature can be altered to suit specific needs.