Reversible inhibition of penicillinase by quinacillin: evaluation of mechanisms involving two conformational states of the enzyme.

Staphylococcal penicillinase (EC 3.5.2.6) is shown to undergo partial, fully reversible inactivation of benzylpenicillinase activity on incubation with the substrate quinacillin, the hydrolysis of which follows a corresponding biphasic time-course. The kinetics fit a scheme involving slow isomerization of the enzyme between conformational states that differ in K_m and V_max for quinacillin. The possibility that inactivation is related to formation of a previously observed covalent enzyme-quinacillin conjugate is ruled out because the kinetics of its formation differ from those of inactivation. This implies that the conjugate arises from a state of the enzyme substrate complex present during the normal catalytic cycle. The multiplicity of binding sites found suggests that a reactive catalytic intermediate substitutes several amino-acid side chains during denaturation of the enzyme-quinacillin mixture, thus providing an explanation of earlier results.     

Identification of a variable region of the African swine fever virus genome that has undergone separate DNA rearrangements leading to expansion of minisatellite-like sequences

Nucleotide sequencing identified a tandemly repeated sequence array 22 x 10(3) base-pairs from the right-hand DNA terminus of the African swine fever virus (ASFV) genome. The sequence of the repeat array and sequences closely flanking it were compared in the genomes of four groups of ASFV isolates that had very different restriction enzyme site maps. Arrays present in one group of ASFV isolates from East Zambia/Malawi varied in length and contained between 8 and 38 copies of a 17-nucleotide repeat unit. Repeat arrays in a second group of ASFV isolates from Europe were less variable in length but consisted of different types of repeat unit that were divergent in sequence. A third genetically diverse ASFV isolate. LIV 13 from a South Zambia Game Park, contained repeat unit types that were similar to those of European viruses. MFUE6 isolate from an East Zambia Game Park contained a shorter version of the European repeat unit. An eight-base-pair core sequence was conserved between the East Zambia/Malawi and European and LIV 13 repeat units. These tandemly repeated sequence arrays share a number of properties with chromosomal minisatellite DNA. Similar tandem repeat arrays have not been described in poxviruses.     

Histamine receptors in the human heart

Histamine receptor subtypes in $\text{in vitro}$ isolated human coronary arteries and in $\text{in vitro}$ human atrial and ventricular myocardium were studied. The H₁ receptor mediates contraction of coronary vascular smooth muscle but has no effect on atrial or ventricular tissue. The H₂ receptor mediates relaxation of human coronary artery vascular smooth muscle and mediates a positive inotropic response in atrial and ventricular myocardium.     

Expression of different mutant p53 transgenes in neuroblastoma cells leads to different cellular responses to genotoxic agents

The involvement of p53 as a determinant of chemosensitivity or radiosensitivity is not well understood and is complicated by numerous contradictory reports. Here we have addressed this issue using a series of isogenic clones derived from two neuroblastoma cell lines that express wild-type p53 genes, Nub7 and IMR32. Two different mutant p53 transgenes were used in an attempt to disrupt p53 function in the clones. Our findings indicate that the cellular response is dependent on the genotoxic agent used as well as on the specific p53 transgene used. Cellular radiosensitivity showed no association with apoptosis or with the ability of the cells to arrest in G1 after irradiation. An association was observed, however, between gamma-radiation sensitivity and DNA double-strand break rejoining activity.     

Complete genome sequence of Anaerococcus prevotii type strain (PC1)

Anaerococcus prevotii (Foubert and Douglas 1948) Ezaki et al. 2001 is the type species of the genus, and is of phylogenetic interest because of its arguable assignment to the provisionally arranged family 'Peptostreptococcaceae'. A. prevotii is an obligate anaerobic coccus, usually arranged in clumps or tetrads. The strain, whose genome is described here, was originally isolated from human plasma; other strains of the species were also isolated from clinical specimen. Here we describe the features of this organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of a member of the genus. Next to Finegoldia magna, A. prevotii is only the second species from the family 'Peptostreptococcaceae' for which a complete genome sequence is described. The 1,998,633 bp long genome (chromosome and one plasmid) with its 1852 protein-coding and 61 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.     

Complete genome sequence of Pirellula staleyi type strain (ATCC 27377)

Pirellula staleyi Schlesner and Hirsch 1987 is the type species of the genus Pirellula of the family Planctomycetaceae. Members of this pear- or teardrop-shaped bacterium show a clearly visible pointed attachment pole and can be distinguished from other Planctomycetes by a lack of true stalks. Strains closely related to the species have been isolated from fresh and brackish water, as well as from hypersaline lakes. Here we describe the features of this organism, together with the complete genome sequence and annotation. This is the first completed genome sequence of the order Planctomyces and only the second sequence from the phylum Planctobacteria/Planctomycetes. The 6,196,199 bp long genome with its 4773 protein-coding and 49 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.