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Query: UNIPROT:P06889 (Mol)
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The minichromosome Ch16 of the fission yeast Schizosaccharomyces pombe is derived from the centromeric region of chromosome III. We show that Ch16 and a shorter derivative, Ch12, made by gamma-ray cleavage, are linear molecules of 530 and 280 kilobases, respectively. Each minichromosome has two novel telomeres, as shown by genomic Southern hybridization with an S. pombe telomere probe. Comparison by hybridization of the minichromosomes and their chromosomal counterparts showed no signs of gross rearrangement. Cosmid clones covering the ends of the long arms of Ch16 and Ch12 were isolated, and subcloned fragments that contained the breakage sites were identified. They are apparently unique in the genome. By hybridization and Bal 31 digestion, the ends appear to consist of the broken-end sequences directly associated with short stretches (about 300 base pairs) of new DNA that hybridizes to a cloned S. pombe telomere. They do not contain the telomere-adjacent repeated sequences that are present in the normal chromosomes. The sizes of the short telomeric stretches are roughly the same as those of the normal chromosomes. Our results show that broken chromosomal ends in S. pombe can be healed by the de novo addition of the short telomeric repeats. The formation of Ch16 must have required two breakage-healing events, whereas a single cleavage-healing event in the long arm of Ch16 yielded Ch12.
Mol Cell Biol 1987 Dec
PMID:Identification of healed terminal DNA fragments in linear minichromosomes of Schizosaccharomyces pombe. 283 Apr 93

Centromeric DNA in the fission yeast Schizosaccharomyces pombe was isolated by chromosome walking and by field inversion gel electrophoretic fractionation of large genomic DNA restriction fragments. The centromere regions of the three chromosomes were contained on three SalI fragments (120 kilobases [kb], chromosome III; 90 kb, chromosome II; and 50 kb, chromosome I). Each fragment contained several repetitive DNA sequences, including repeat K (6.4 kb), repeat L (6.0 kb), and repeat B, that occurred only in the three centromere regions. On chromosome II, these repeats were organized into a 35-kb inverted repeat that included one copy of K and L in each arm of the repeat. Site-directed integration of a plasmid containing the yeast LEU2 gene into K repeats at each of the centromeres or integration of an intact K repeat into a chromosome arm had no effect on mitotic or meiotic centromere function. The centromeric repeat sequences were not transcribed and possessed many of the properties of constitutive heterochromatin. Thus, S. pombe is an excellent model system for studies on the role of repetitive sequence elements in centromere function.
Mol Cell Biol 1988 Feb
PMID:Structural organization and functional analysis of centromeric DNA in the fission yeast Schizosaccharomyces pombe. 283 35

Several members of a repetitive DNA family in the nematode Caenorhabditis elegans have been shown to express ARS and centromeric function in Saccharomyces cerevisiae. The repetitive family, denoted CeRep3, consists of dispersed repeated elements about 1 kilobase in length, present 50 to 100 times in the nematode genome. Three elements were sequenced and found to contain DNA sequences homologous to yeast ARS and CEN consensus sequences. Nematode DNA segments containing these repeats were tested for ARS and CEN (or SEG) function after ligation to shuttle vectors and introduction into yeast cells. Such nematode segments conferred ARS function to the plasmid, as judged by an increased frequency of transformation compared with control plasmids without ARS function. Some, but not all, also conferred to the plasmid increased mitotic stability, increased frequency of 2+:2- segregation in meiosis, and decreased plasmid copy number. These effects are similar to those of yeast centromeric DNA. In view of these results, we suggest that the CeRep3 repetitive family may have replication and centromeric functions in C. elegans.
Mol Cell Biol 1988 Feb
PMID:Nematode repetitive DNA with ARS and segregation function in Saccharomyces cerevisiae. 283 41

The genomic environments of six unrelated variant surface glycoprotein (VSG) gene families in the IsTaR 1 serodeme of Trypanosoma brucei were examined by Southern blot analysis of DNA resolved by conventional and pulse field gradient electrophoresis. The genomic locations of these gene family members were characterized in variants arising from 19 independent antigenic switches of which 13 represent single relapses. We have identified 9 distinct telomeric sites containing VSG genes on 7 different chromosomes ranging in size from approximately 65 kilobase pairs to greater than 3 megabase pairs. VSG genes are expressed in at least 6 of these telomeric sites. All of the observed antigenic switches can be explained by two types of processes: gene conversion and telomeric activation, with almost half (9/19) the result of combinations of these processes. The implications of these observations are discussed with particular reference to the frequencies of occurrence of each process.
Mol Biochem Parasitol 1988 Jun
PMID:Multiple events associated with antigenic switching in Trypanosoma brucei. 284 74

In the IsTaR 1 serodeme, we have identified variant surface glycoprotein (VSG) genes in nine different telomeric sites. We have measured the distance from the 3' end of these VSG genes to the end of the chromosome (the 'telomere length') in 20 variant antigen types (VATs) of the serodeme. Analyses of the changes in telomere length during 19 antigenic switches involving eight telomeric sites indicate a median increase in telomere length of 0.6 kilobase pairs during each switch. This may be accounted for by the 6-10 bp increase in telomere length per generation associated with DNA replication described by others. The changes in telomere lengths do not form a normal distribution since a substantial fraction show unusually large increases in telomere length or decreases in telomere length during an antigenic switch. These changes are probably caused by recombinations 3' to the VSG gene. No significant differences were detected in the behavior of telomeres at each of the eight different telomeric sites, nor were changes in telomere lengths significantly different between different antigenic switches. However, it was found that those telomeres where transcription was activated during the antigenic switch showed a significantly greater increase in telomere length than those telomeres not involved in regulation of VSG gene expression. Conversely, there was a strong correlation between transcriptional inactivation of a telomeric expression site and a decrease in telomere length. These findings suggest that processes (possibly genomic recombinations) 3' to the VSG gene coding region may be associated with a change in the transcriptional status of the VSG gene.
Mol Biochem Parasitol 1988 Jun
PMID:Changes in telomere length associated with antigenic variation in Trypanosoma brucei. 284 75

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction-fragment-length polymorphism allele (RFLP) of the telomeric alpha-globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t-haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.
Mol Biol Evol 1988 Mar
PMID:Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes. 289 63

Antigenic switching in Trypanosoma brucei can occur either by the production of a telomeric copy of a variant surface glycoprotein (VSG) gene through a gene conversion mechanism or by the nonduplicative activation of a telomeric VSG gene. The 5 VSG gene telomeric copy that is expressed in IsTaR 1 variant antigenic type (VAT) 5 is retained in an inactive state following an antigenic switch to VAT A5. This inactive telomeric 5 VSG gene copy is absent following independent single antigenic switches to VATs 1A5 and 11A5. The inactive 5 VSG gene does not appear to have been replaced with the newly expressed VSG gene. Thus, inactive telomeric VSG genes that are capable of being expressed can be lost, presumably through gene conversion to new VSG genes. These results suggest that gene conversion of an inactive VSG gene does not obligately activate the new VSG gene. We conclude that the gene conversion and telomeric activation mechanisms for antigenic switching are separate and independent processes.
Mol Biochem Parasitol 1985 Jun
PMID:The two mechanisms for antigenic variation in Trypanosoma brucei are independent processes. 299 80

Three tetramers of the 170 base-pair monomer repeat unit of human centromeric DNA (alphoid DNA) have been cloned and sequenced. Adjacent subunits differed in sequence by 30 to 45%, while dimers varied by 13 to 20% whether adjacent or not. Divergence was distributed unevenly across the monomeric sequence, such that two highly conserved segments adjoined clusters of insertions/deletions. Divergence, calculated from the cloned sequences or measured in uncloned DNA by thermal destabilization of mismatched reassociated duplexes, was far greater than previously estimated for the total human alphoid family. The population of these repeats within the human genome was not uniformly diverged, however, since restriction subsets of alphoid DNA contained as little as one-tenth the overall level of divergence. This indicates a hierarchical or familial structure of the genomic repeat population. Using cloned probes, human alphoid DNA was shown to be highly methylated and transcriptionally inactive. These data, along with evidence of conserved segments and periodicities (dimeric and higher-order) overlying considerable sequence diversity, support a structural role for this DNA family.
J Mol Biol 1985 Nov 05
PMID:Human alphoid family of tandemly repeated DNA. Sequence of cloned tetrameric fragments and analysis of familial divergence. 300 16

The ability of the plasmid pE194 from S. aureus to serve as an autonomously replicating sequence (ARS) in yeast was shown. The hybrid plasmid pLD744 that contains pE194 and the yeast LEU2 gene sequences is unstable in yeast like other YRp-vectors: the mitotic stability of the pLD744 was as much as 1%. The plasmid pLD712 that differs from pLD744 by the existence of a centromeric sequence from the chromosome III of yeast Saccharomyces cerevisiae reveals about one order greater stability. The observation that there are some sequences in the primary structure of the pE194 which strongly conform to the ARS consensus in yeast inclines us to infer that the existence of ARS consensus on pE194 DNA is not sufficient for its effective replication in yeast.
Mol Biol (Mosk)
PMID:[Replication in yeasts of plasmid pE194 from Staphylococcus aureus]. 300 42

Analysis of rhesus monkey alphoid DNA suggests that it arose by tandem duplication of an ancestral monomer unit followed by independent variation within two adjacent monomers (one becoming more divergent than the other) before their amplification as a dimer unit to produce tandem arrays. The rhesus monkey alphoid DNA is a tandemly repeated, 343-bp dimer; the consensus dimer is over 98% homologous to the alphoid dimers reported for baboon and bonnet monkey, 81% homologous to the African green monkey alpha monomer, and less than 70% homologous to the more divergent human alphoid DNAs. The consensus dimer consists of two wings (I and II, 172 and 171 bp, respectively) that are only 70% homologous to each other, but share seven regions of exact homology. These same regions are highly conserved among the consensus sequences of the other cercopithecid alphoid DNAs. The three alpha-protein binding sites reported for African green monkey alpha DNA by F. Strauss and A. Varshavsky (Cell 37: 889-901, 1984) occur in wings I and II, but with one site altered in wing I. Two cloned dimer segments are 98% homologous to the consensus, each containing 8 single-base-pair differences within the 343-bp segment. Surprisingly, 37% of these differences occur in regions that are evolutionarily conserved in the alphoid consensus sequences, including the alpha-protein binding sites. Sequence variation in this highly repetitive DNA family may produce unique nucleosomal architectures for different members of an alphoid array. These unique architectures may modulate the evolution of these repetitive DNAs and may produce unique centromeric characteristics in primate chromosomes.
J Mol Evol 1986
PMID:Sequence and evolution of rhesus monkey alphoid DNA. 301 69


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