RESUMEN
A method is described which permits the ligation- mediated PCR amplification of specific fragments from a Class-II restriction endonuclease total digest. Feasibility was tested using Bcl I and phage lambda DNA as a model enzyme and amplicon system, respectively. Bcl I is one of many widely used restriction enzymes which cleave at palindromic recognition sequences and leave 5'-protruding ends of defined sequence. Using a single pair of universal primers, a given fragment can be specifically amplified after joining the fragments to adaptors consisting of a duplex primer region and a 9-nucleotide protruding single-stranded 5'-end containing the sequence complementary to the cleaved restriction site and a 4-nucleotide 'indexing sequence.' The protruding strand anneals to a restriction fragment by displacing its corresponding strand in the same fragment-specific indexing sequence located juxtaposed to the restriction site. The adaptor is covalently linked to the restriction fragment by T4 DNA ligase, and amplification is carried out under conditions for long-distance PCR using the M13 forward and reverse primers. The technique discriminated robustly between mismatches and perfect matches for the 16 indexing sequences tested to allow individual lambda Bcl I fragments to be amplified from their respective adaptor pairs. A strategy is proposed enabling a non-cloning approach to the accession, physical mapping and sequencing of genomic DNA. The method could also have application in high-throughput genetic mapping and fingerprinting and should expand the enzyme base for ligation- mediated indexing technology which has previously been limited to the Class-IIS and IP restriction endonucleases.
Asunto(s)
Bacteriófago lambda/genética , ADN Viral/metabolismo , Desoxirribonucleasas de Localización Especificada Tipo II/metabolismo , Reacción en Cadena de la PolimerasaRESUMEN
Paramecium tetraurelia stock 51 can express at least 11 different types of surface antigens, yet only a single type is expressed on the surface of an individual cell at any one time. The differential expression of stock 51 type A and B surface antigen genes (51A and 51B) is regulated at the level of transcription. Previously, we reported that nucleotide sequences upstream of position -26 (relative to the start of translation) in the 51A and 51B surface antigen genes are necessary for transcriptional activity but are not sufficient to direct differential transcriptional control. In this report we demonstrate that at least some of the critical elements necessary for differential transcription of the 51A and 51B genes lie within the 5' coding region. A hybrid gene that contains 51B upstream sequences (-475 to +1) attached to the ATG start codon of 51A is not cotranscribed with the 51B gene. In contrast, further substitution with 51B sequences (-1647 to +885) allows the chimeric gene to be coexpressed with 51B. A different hybrid gene containing a substitution of 51B sequence from -26 to +885 in the 51A gene is also coexpressed with 51B, revealing that the critical elements within the coding region of 51B do not require 51B upstream sequences for their effect. Coinjection of the 51A gene with the chimeric gene that contains 51B up to +885 showed that the same sequences that allow coexpression with 51B prevent cotranscription with 51A. Together, these results demonstrate that a region downstream of the transcriptional start site between nucleotide positions +1 and +885 (relative to translational start) is necessary to control differential transcriptional activity.
Asunto(s)
Antígenos de Protozoos/genética , Antígenos de Superficie/genética , Regulación de la Expresión Génica , Genes Protozoarios , Paramecium tetraurelia/genética , Transcripción Genética , Animales , Antígenos de Protozoos/biosíntesis , Antígenos de Superficie/biosíntesis , Secuencia de Bases , Núcleo Celular/metabolismo , Cartilla de ADN , Sondas de ADN , Datos de Secuencia Molecular , Paramecium tetraurelia/metabolismo , Plásmidos , Reacción en Cadena de la Polimerasa , Biosíntesis de Proteínas , ARN Protozoario/biosíntesis , Secuencias Reguladoras de Ácidos NucleicosRESUMEN
Paramecium tetraurelia stock 51 can express at least 11 different surface antigens, yet only one type is found on the surface of a cell at any given time. The mechanism that controls this mutually exclusive expression is unknown. A previous study has shown that the 51A surface antigen gene is regulated at the level of transcription (Gilley, D., Rudman, B. M., Preer, J. R., Jr., and Polisky, B. (1990) Mol. Cell. Biol. 10, 1538-1544). We show here that the 51B surface antigen gene is also transcriptionally regulated, and when the 51A and 51B genes are cotransformed into an A-, B- mutant, the 51A antigen is dominant at 27 degrees C just as in wild type cells. We have utilized this cotransformation system to experimentally determine that 273 base pairs of DNA upstream of the 51A gene is sufficient to allow the dominant expression of A, but 150 base pairs is not adequate. A hybrid gene that contains the upstream region of 51B attached to the 51A transcribed region was cotransformed with the 51B gene into the A-, B- mutant. Despite containing the same upstream sequences, only the hybrid 51B/A was transcribed at 27 degrees C. These results suggest the upstream region is required but not sufficient for mutually exclusive transcriptional control.
Asunto(s)
Antígenos de Protozoos/genética , Antígenos de Superficie/genética , Genes Protozoarios , Paramecium tetraurelia/inmunología , Animales , Regulación de la Expresión Génica/genética , Paramecium tetraurelia/genética , Eliminación de Secuencia , Transcripción GenéticaRESUMEN
Paramecium tetraurelia contains two types of nuclei, a diploid germinal micronucleus and a large transcriptionally active macronucleus. The macronuclear genome is formed from the micronuclear DNA during sexual reproduction. Previous studies have shown that the processing of the A-type variable surface protein gene during formation of a new macronucleus is dependent on the presence of the A gene in the old macronucleus. It is not clear if this is a general feature that controls the formation of the Paramecium macronuclear genome or a unique feature of the A locus. Using micronuclear transplantation, we have constructed a strain that has a wild-type micronucleus but has macronuclear deletions of the A- and B-type surface protein genes. Neither the A nor the B gene is incorporated into the new macronucleus after sexual reproduction. Macronuclear transformation of this strain with the B gene rescues the B-gene deletion after formation of the next macronucleus but has not effect on the A deletion. Similarly, transformation with the A gene shows gene-specific rescue for A but not B. The effect of the old macronucleus on the processing of the new macronucleus results in a pattern of non-Mendelian inheritance of both macronuclear deletions. Progeny from the wild-type exconjugant are all wild type, and progeny from the A- B- exconjugant are mutant. The features of this A- B- non-Mendelian mutant demonstrate that the regulation of macronuclear DNA processing is gene specific, and our results open the possibility that this type of regulation affects many regions of the Paramecium genome.