摘要:

SummaryThe clostridial neurotoxins responsible for tetanus and botulism are metallo‐proteases that enter nerve cells and block neurotransmitter release via zinc‐dependent cleavage of protein components of the neuroexocytosis apparatus. Tetanus neurotoxin (TeNT) binds to the presynaptic membrane of the neuromuscular Junction and is internalized and transported retroaxonally to the spinal cord. Whilst TeNT causes spastic paralysis by acting on the spinal inhibitory interneurons, the seven serotypes of botullnum neurotoxins (BoNT) induce a flaccid paralysis because they intoxicate the neuromuscular junction. TeNT and BoNT serotypes B, D, F and G specifically cleave VAMP/synaptobrevin, a membrane protein of small synaptic vesicles, at different single peptide bonds. Proteins of the presynaptic membrane are specifically attacked by the other BoNTs: serotypes A and E cleave SNAP‐25 at two different sites located within the carboxyl terminus, whereas the specific target of serotype C is syn

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00396.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryDeinococcus radioduransand other members of the same genus share extraordinary resistance to the lethal and mutagenic effects of ionizing and u.v. radiation and to many other agents that damage DNA. While it is known that this resistance is due to exceedingly efficient DNA repair, the molecular mechanisms responsible remain poorly understood. Following very high exposures to u.v. irradiation (e.g. 500 Jm−2, which is non‐lethal toD. radiodurans), this organism carries out extremely efficient excision repair accomplished by two separate nucleotide excision repair pathways acting simultaneously. One pathway requires theuvrAgene and appears similar to the UvrABC excinuclease pathway defined inEscherichia coli.The other excision repair pathway is specific for u.v. dimeric photoproducts, but is not mediated by a pyrimidine dimer DNA glycosylase. Instead, it is initiated by a second bona fide endonuclease that may recognize both pyrimidine dimers and pyrimidine‐(6–4)pyrimidones. After high doses of ionizing‐radiation (e.g. 1.5Mrad),D. radioduranscan mend>100 double‐strand breaks (dsb) per chromosome without lethality or mutagenesis. Both dsb mending and survival arerecA‐dependent, indicating that efficient dsb mending proceeds via homologous recombination.D. radioduranscontains multiple chromosomes per cell, and it is proposed that dsb mending requires extensive recombination amongst these chromosomes, a novel phenomenon in bacteria. Thus,D. radioduransmay serve as an easily accessible model system for the double‐strand‐break‐initiated interchromosomal recombination that occurs in eukaryotic cells during

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00397.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryDNA synthesis is an accurate and very processive phenomenon, yet chromosome replication does not proceed at a constant rate and progression of the replication fork can be impeded. Several structural and functional features of the template can modulate the rate of progress of the replication fork. These include DNA secondary structures, DNA damage and occupied protein‐binding sites. In addition, prokaryotes contain sites where replication is specifically arrested. DNA regions at which the replication machinery is blocked or transiently slowed could be particularly susceptible to genome rearrangements. Illegitimate recombination, a ubiquitous phenomenon which may have dramatic consequences, occurs by a variety of mechanisms. The observation that some rearrangements might be facilitated by a pause in replication could provide a clue in elucidating these processes. In support of this, some homologous and illegitimate recombination events have already been correlated with replication pauses or arrest site

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryInSynechococcusspecies PCC7942, the production of a subset of proteins is induced when it is grown in a phosphate‐limited medium. We previously suggested that a pair of cyanobacterial two‐component regulatory proteins, SphS (sensory‐kinase) and SphR (response‐regulator), may be involved in this particular response to phosphate limitation. Here it was found that a protein with an apparent molecular mass of 33 kDa became particularly abundant when the total cellular proteins from cells grown in a phosphate‐limited medium were analysed by SDS‐PAGE. A deletion mutant lacking both thesphSand thesphRgenes failed to produce this 33 kDa protein in response to phosphate limitation. Thus it was reasonable to assume that this protein is a member of the group of proteins involved in theSynechococcusphosphate regulatory circuit (hence, it was named SphX). The SphX protein was purified to near homogeneity, and the corresponding structural gene was cloned. The determined nucleotide sequence revealed that thesphXgene encodes a novel protein with a calculated molecular mass of 36 374 Da, which was demonstrated to be located in the cytoplasmic membrane. Structural features of theSphXpromoter were then clarified by determining its transcription start site, from which transcription was triggered in response to phosphate limitation. Furthermore, the putative response‐regulator, SphR, was demonstrated to bind to the upstream region of theSphXpromoter by means ofin vitroDNase I footprinting. From these results, we conclude that thesphXgene is a member of theSynechococcusphosphate regulatory circuit, in which the two signal‐transduction components, SphS and SphR, are crucially involved as transcriptional regulators. The SphX protein may play a role in phosphate assimilation

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe region immediately downstream from themiaAtRNA modification gene at 94.8 min contains thehfqgene and thehflAregion, which are important in the bacteriophage Qβ and lambda life cycles. The roles of these genes in bacteria remain largely unknown. We report here the characterization of two chromosomalhfqinsertion mutations. An omega (ω) cassette insertion near the end ofhfqresulted in phenotypes only slightly different from the parent, although transcript mapping demonstrated that the insertion was completely polar onhfqexpression. In contrast, an equally polar omega cassette insertion near the beginning ofhfqcaused pronounced pleiotropic phenotypes, including decreased growth rates and yields, decreased negative supercoiling of piasmids in stationary phase, increased cell size, osmosensitivity, increased oxidation of carbon sources, increased sensitivity to ultraviolet light, and suppression ofbglactivation byhnsmutations,hfq::ω mutant phenotypes were distinct from those caused by omega insertions early in themiaAtRNA modification gene. On the other hand, bothhfqinsertions interfered with lambda phage plaque formation, probably by means of polarity at thehflAregion. Together, these results show thathfqfunction plays a fundamental role inEscherichia coliphysiology and thathfqand thehflAregion are in theamiB‐mutL‐miaA‐hfq‐hflXs

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryRhizobium melilotiDctD is believed to have three functional domains: anN‐terminal, two‐component receiver domain; and like other σ54‐dependent activators,C‐terminal and central domains for DNA binding and transcription activation. We have characterized a progressive series of M‐terminal deletions ofR melilotiDctD. TheN‐terminal domain was not needed for binding the dctA upstream activation sequence. Only 25% of theC‐terminal end of the receiver domain was needed to significantly inhibit the central domain, and proteins lacking up to 60% of theN‐terminal end of the receiver domain were‘inducible’inR. meliloticells. We hypothesize that the W‐terminal two‐thirds of the DctD receiver domain augments and controls an adjacent subdomain for inhib

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00401.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SumnnaryAn extracellular particle approximately 40 nM in diameter was detected in culture supernatant from the fastidious bacteriumRochalimaea henselae.This particle has at least three associated proteins and contains 14kbp linear DNA segments that are heterogeneous in sequence. The 14kbp DNA was also present inR. henselaecells as an extrachromosomal element for all 14 strains tested. Despite attempts to induce lysis ofR henselae, plaque formation was not observed. A similar particle, also containing 14 kbp DNA, was observed inBartonella bacilliformis, and may be analogous to a bacteriophage that has been described elsewhere forB. bacilliformis.

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00402.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryAntigenic variation of theNeisseria gonorrhoeaepilus occurs when a variant pilin sequence from a silent locus recombines into the expression locus by predominantly unidirectional, homologous recombination. At the 3’end of all pilin loci lies a conserved ONA sequence, called the Sma/Cla repeat, which has sequence similarity to several recombinase‐binding sites, and therefore may be involved in pilin recombination. We have developed a novel reverse transcriptase/polymerase chain reaction (RT‐PCR) assay for direct monitoring of pilin recombination, and both RT‐PCR and phase variation were used to examine pilin recombination in a gonococcal strain that had had thepilESma/Cla repeat removed. Results from these experiments showed a decrease in pilin recombination when the Sma/Cla sequence was deleted from the expression locus, showing that a specialized site (Sma/Cla) is involved in efficient pilin recomb

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00403.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryHydroxylamine (HA) mutagenesis of an HA‐induced splicing‐defective bacteriophage T4tdintron mutant with a mutation in the intron P3 RNA pairing region was used to generate pseudorevertants. Because HA can only cause GC to AT transitions, the original mutant (H104A) could not undergo true reversion, yet the compensatory mutation on the opposite side of the P3 helix, which was complementary to the original H104A mutation, could occur. A pseudorevertant was isolated that contained both the original H104A mutation and the compensatory mutation HS9. By phenotypic and molecular genetic criteria, this double mutant (H104A‐HS9) was shown to be able to undergo significant RNA splicing, thus confirming the existence and functional importance of the long‐range P3 pairing region in this phage intron. The second‐site suppressor mutation (HS9) was isolated by phage cross and also exhibited some self‐splicing ability. A correlation exists between the strength of P3 helix Watson‐Crick base pairing and the apparent level of splicing when wild‐type, H104A, HS9, and H104A‐HS9 are compared. This suggests that the primary role of the P3 RNA pairing region in the T4tdintron is structural in contributing to the critical RNA se

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00404.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

SummaryThe promoter region of thecryIIIAtoxin gene ofBacilius thuringiensisis composed of at least three domains: an upstream region extending from nucleotide positions ‐635 to ‐553 (with reference to the translational start codon ofcryIIIA), an internal region extending from nucleotide positions ‐553 to ‐367, and a downstream region extending from nucleotide position 367 to +18. Deletion analysis and transcriptional fusions to thelacZgene indicate that full expression ofcryIIIArequires the association of the upstream and the downstream region. Primer extension experiments reveal a majorcryIIIAtranscript (designated T‐129) starting at nucleotide position ‐129 and another transcript (designated T‐558) starting at nucleotide position ‐558. Mutation in the ‐35 region of the promoter responsible for the initiation of T‐558 indicates that the upstream promoter is essential for full expression ofcryIIIA, although not sufficient. Deletion of the DNA region carrying the previously describedcryIIIApromoter does not affect full expression ofcryIIIAand does not modify the 5 end of T‐129. Taken together, these results indicate that the 5 end of T‐129 is not a transcriptional start site. Therefore, we propose that T‐129 results from the processing of the mRNA initiated at the upstream promoter (T‐558), generating a stable mRNA with a 5’extremity at nucleotide position ‐129. From primer extension analysis and transcriptional fusions tolacZ, it appears that the upstream promoter is weakly but significantly expressed during the vegetative phase of growth, is activated at the onset of sporula‐tion and remains active at least until t5. However, unlike the promoters of other cry genes, this promoter is similar to σa‐dependent promoters rather than sporulation‐specific promoters. This promoter may therefore be transcribed by the EσAform of RNA polymerase. Activation at the onset of sporulation could result from the disappearance of a repressor, or the appearance o

ISSN:0950-382X    

DOI:10.1111/j.1365-2958.1994.tb00405.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY