RESUMO
Factors other than molecular weight are known to affect DNA electrophoretic mobility. DNA methylation has been found to affect the curvature of DNA, causing anomalous mobility in polyacrylamide gels; the effect of methylation on the mobility of large DNA molecules in agarose gels was unknown. Chromosomal DNA from Mycoplasma capricolum, a wall-less prokaryote which has a low intrinsic methylation rate, was methylated in agarose blocks by SssI methylase, a de novo methylase with a CpG recognition sequence. (A surprising finding was that SssI methylase altered the structure of InCert, but not SeaKem Gold, agarose.) Restriction enzyme analysis was used to estimate the extent of CpG methylation. DNA methylation was found to have no effect on the electrophoretic mobility of full-length chromosomal DNA (1,120 kbp) in agarose gels. Therefore, methylation is not a source of error in PFGE-based size estimation for chromosomal DNA molecules less than 1.12 Mbp in agarose gels.
Assuntos
Cromossomos Bacterianos , Metilação de DNA , DNA Bacteriano/isolamento & purificação , Eletroforese em Gel de Ágar/métodos , Eletroforese em Gel de Campo Pulsado/métodos , Mycoplasma/genética , DNA-Citosina Metilases/metabolismo , Desoxirribonuclease HpaII/metabolismoRESUMO
OBJECTIVE: To determine central nervous system (CNS) involvement in acutely disseminated Borrelia burgdorferi infection by measurement of borrelia-specific DNA using the polymerase chain-reaction (PCR) assay and to compare the results of this with standard serological tests. DESIGN: Prospective study with laboratory investigators blinded to clinical data. SETTING: Multicenter office practice with a central reference laboratory. PATIENTS: Cerebrospinal fluid (CSF) was collected from 12 patients with acute disseminated Lyme borreliosis with less than 2 weeks of active disease. The normal control specimens came from 16 patients whose CSF samples had been sent to the clinical laboratory for tests unrelated to the present study. MAIN OUTCOME MEASURES: Clinical evidence of disease and laboratory abnormalities. RESULTS: Eight of the 12 patients (four of six with multiple areas of erythema migrans and four of six with cranial neuritis without erythema migrans) had B burgdorferi-specific DNA in their CSF. Among the 12 patients studied, nine had acute cranial neuritis and six had multiple erythema migrans lesions. Just four of the eight who were found to have spirochetal DNA in their CSF had complaints suggestive of CNS infection. In three of the PCR-positive CSF samples, no other abnormalities were noted. None of 16 samples from controls were positive in the PCR assay. CONCLUSION: B burgdorferi can invade the CNS early in the course of infection. Careful consideration should be given to choosing antibiotics that achieve adequate CSF levels in patients with disseminated infection.
Assuntos
Grupo Borrelia Burgdorferi/isolamento & purificação , Doenças do Sistema Nervoso Central/microbiologia , Doença de Lyme/microbiologia , Anticorpos Antibacterianos/análise , Sequência de Bases , Grupo Borrelia Burgdorferi/genética , Grupo Borrelia Burgdorferi/imunologia , Doenças do Sistema Nervoso Central/líquido cefalorraquidiano , Líquido Cefalorraquidiano/microbiologia , DNA Bacteriano/análise , Humanos , Doença de Lyme/líquido cefalorraquidiano , Dados de Sequência Molecular , Reação em Cadeia da Polimerase , Estudos ProspectivosRESUMO
Full-size linear chromosomes were prepared from mycoplasmas by using gamma-irradiation to introduce one (on average) double-strand break in their circular chromosomes. Chromosome sizes were estimated by pulsed-field gel electrophoresis (PFGE) from the mobilities of these full-length molecules relative to DNA size references. Sizes estimated for Ureaplasma urealyticum T960 and 16 Mycoplasma species ranged from 684 kbp (M. hominis) to 1315 kbp (M. iowae). Using this sample, we found no correlation between the mobility of the full-size linear chromosomes and their G + C content. Sizes for A. laidlawii and A. hippikon were within the range expected from renaturation kinetics. PFGE size estimates are in good agreement with sizes determined by other methods, including electron microscopy, an ordered clone library, and summation of restriction fragments. Our estimates also agree with those from renaturation kinetics for both the largest and some of the smallest chromosomes, but in the intermediate size range, renaturation kinetics consistently provides lower values than PFGE or electron microscopy. Our PFGE estimates show that mycoplasma chromosomes span a continual range of sizes, with several intermediate values falling between the previously recognized large and small chromosome size clusters.
Assuntos
Acholeplasma/genética , Cromossomos Bacterianos/ultraestrutura , Mycoplasma/genética , Ureaplasma/genética , Acholeplasma laidlawii/genética , Composição de Bases , Cromossomos Bacterianos/efeitos da radiação , DNA Bacteriano/análise , Densitometria , Eletroforese , Raios gama , Cinética , Microscopia EletrônicaRESUMO
An actin-like protein has been identified in cell extracts from the prokaryote Mycoplasma pneumoniae. This protein bears a striking resemblance to actin from vertebrates: (i) the solubility of the protein during isolation is analogous to that of actin bound to myosin (soluble in high ionic strength salt solution and insoluble at low ionic strength), (ii) sodium dodecyl sulfate treatment of the partially purified M. pneumoniae extract produces a protein with an electrophoretic mobility very close to that of vertebrate actin in sodium dodecyl sulfate/polyacrylamide gels, (iii) treatment of preparations with ATP-Mg2+ allows separation of long curvilinear filaments, 5-6 nm wide, that closely resemble eukaryotic filamentous actin, and (iv) the prokaryotic filamentous actin binds vertebrate heavy meromyosin fragments to form hybrid compleexes with the characteristic shape of periodic repeating arrowheads, and no heavy meromyosin is bound in the presence of ATP.
