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PubMed1997

Replication and segregation of a miniF plasmid during the division cycle of Escherichia coli.

Replication of the miniF plasmid pML31 was examined during the division cycle of Escherichia coli growing with doubling times between 40 and 90 min at 37 degrees C and compared to the replication of plasmid pBR322 and the minichromosome pAL70. The replication pattern of pML31 was indistinguishable from that of pBR322 at all growth rates and very different from the cell-cycle-specific replication of the minichromosome. It is concluded that both pML31 and pBR322 plasmids can replicate at all stages of the division cycle, with a probability of replication that increases gradually, but perhaps not exponentially, during the cycle. In contrast, the modes of segregation of pML31 and pBR322 plasmids into daughter cells at division appeared to differ, raising the possibility that pML31 may segregate in a nonrandom fashion similar to that of chromosomes and minichromosomes.

Cell Division↗
PubMed2005

Protein diversity confers specificity in plasmid segregation.

The ParG segregation protein (8.6 kDa) of multidrug resistance plasmid TP228 is a homodimeric DNA-binding factor. The ParG dimer consists of intertwined C-terminal domains that adopt a ribbon-helix-helix architecture and a pair of flexible, unstructured N-terminal tails. A variety of plasmids possess partition loci with similar organizations to that of TP228, but instead of ParG homologs, these plasmids specify a diversity of unrelated, but similarly sized, partition proteins. These include the proteobacterial pTAR, pVT745, and pB171 plasmids. The ParG analogs of these plasmids were characterized in parallel with the ParG homolog encoded by the pseudomonal plasmid pVS1. Like ParG, the four proteins are dimeric. No heterodimerization was detectable in vivo among the proteins nor with the prototypical ParG protein, suggesting that monomer-monomer interactions are specific among the five proteins. Nevertheless, as with ParG, the ParG analogs all possess significant amounts of unordered amino acid residues, potentially highlighting a common structural link among the proteins. Furthermore, the ParG analogs bind specifically to the DNA regions located upstream of their homologous parF-like genes. These nucleoprotein interactions are largely restricted to cognate protein-DNA pairs. The results reveal that the partition complexes of these and related plasmids have recruited disparate DNA-binding factors that provide a layer of specificity to the macromolecular interactions that mediate plasmid segregation.

Bacterial Proteins↗
PubMed2005

cse, a Chimeric and variable gene, encodes an extracellular protein involved in cellular segregation in Streptococcus thermophilus.

The isolation of a Streptococcus thermophilus CNRZ368 mutant displaying a long-chain phenotype allowed us to identify the cse gene (for cellular segregation). The N terminus of Cse exhibits high similarity to Streptococcus agalactiae surface immunogenic protein (SIP), while its C terminus exhibits high similarity to S. thermophilus PcsB. In CNRZ368, deletion of the entire cse open reading frame leads to drastic lengthening of cell chains and altered colony morphology. Complementation of the Deltacse mutation with a wild-type allele restored both wild-type phenotypes. The central part of Cse is a repeat-rich region with low sequence complexity. Comparison of cse from CNRZ368 and LMG18311 strains reveals high variability of this repeat-rich region. To assess the impact of this central region variability, the central region of LMG18311 cse was exchanged with that of CNRZ368 cse. This replacement did not affect chain length, showing that divergence of the central part does not modify cell segregation activity of Cse. The structure of the cse locus suggests that the chimeric organization of cse results from insertion of a duplicated sequence deriving from the pcsB 3' end into an ancestral sip gene. Thus, the cse locus illustrates the module-shuffling mechanism of bacterial gene evolution.

Cell Compartmentation↗
PubMed1981

Genetic mapping of endogenous mouse mammary tumor viruses: locus characterization, segregation, and chromosomal distribution.

The restriction endonuclease EcoRI has been used to study the inheritance of strain difference in endogenous mouse mammary tumor virus DNA sequences. This enzyme, which cleaves at only one site within the nondefective viral genome, generates DNA fragments containing mouse mammary tumor virus sequences which vary in size according to the locations of EcoRI restriction sites in the flanking mouse sequences, thereby defining unique integration sites of the viral genome. Recombinant inbred strains of mice have been used to study the inheritance of these DNA fragments which hybridize to mouse mammary tumor virus cDNA sequences. The results define 11 segregating units consisting of 1 or 2 fragments. These units were shown to segregate among the recombinant inbred strains, and in some instances linkage was established. Two units were shown to be linked on chromosome 1. Another unit was mapped to chromosome 7, which is presumably identical to the previously defined genetic locus Mtv- 1. One other mouse mammary tumor virus locus was tentatively assigned to chromosome 6. The results are consistent with the view that integration of mouse mammary tumor virus can take place at numerous sites within the genome, and once inserted, these proviruses appear to be relatively stable genetic entities.

Animals↗
PubMed1991

In vivo analysis of the Saccharomyces cerevisiae centromere CDEIII sequence: requirements for mitotic chromosome segregation.

In the yeast Saccharomyces cerevisiae, the complete information needed in cis to specify a fully functional mitotic and meiotic centromere is contained within 120 bp arranged in the three conserved centromeric (CEN) DNA elements CDEI, -II, and -III. The 25-bp CDEIII is most important for faithful chromosome segregation. We have constructed single- and double-base substitutions in all highly conserved residues and one nonconserved residue of this element and analyzed the mitotic in vivo function of the mutated CEN DNAs, using an artificial chromosome. The effects of the mutations on chromosome segregation vary between wild-type-like activity (chromosome loss rate of 4.8 x 10(-4)) and a complete loss of CEN function. Data obtained by saturation mutagenesis of the palindromic core sequence suggest asymmetric involvement of the palindromic half-sites in mitotic CEN function. The poor CEN activity of certain single mutations could be improved by introducing an additional single mutation. These second-site suppressors can be found at conserved and nonconserved positions in CDEIII. Our suppression data are discussed in the context of natural CDEIII sequence variations found in the CEN sequences of different yeast chromosomes.

Base Sequence↗
PubMed1993

A mutation in PLC1, a candidate phosphoinositide-specific phospholipase C gene from Saccharomyces cerevisiae, causes aberrant mitotic chromosome segregation.

We identified a putative Saccharomyces cerevisiae homolog of a phosphoinositide-specific phospholipase C (PI-PLC) gene, PLC1, which encodes a protein most similar to the delta class of PI-PLC enzymes. The PLC1 gene was isolated during a study of yeast strains that exhibit defects in chromosome segregation. plc1-1 cells showed a 10-fold increase in aberrant chromosome segregation compared with the wild type. Molecular analysis revealed that PLC1 encodes a predicted protein of 101 kDa with approximately 50 and 26% identity to the highly conserved X and Y domains of PI-PLC isozymes from humans, bovines, rats, and Drosophila melanogaster. The putative yeast protein also contains a consensus EF-hand domain that is predicted to bind calcium. Interestingly, the temperature-sensitive and chromosome missegregation phenotypes exhibited by plc1-1 cells were partially suppressed by exogenous calcium.

Amino Acid Sequence↗
PubMed1994

DBF8, an essential gene required for efficient chromosome segregation in Saccharomyces cerevisiae.

To investigate chromosome segregation in Saccharomyces cerevisiae, we examined a collection of temperature-sensitive mutants that arrest as large-budded cells at restrictive temperatures (L. H. Johnston and A. P. Thomas, Mol. Gen. Genet. 186:439-444, 1982). We characterized dbf8, a mutation that causes cells to arrest with a 2c DNA content and a short spindle. DBF8 maps to chromosome IX near the centromere, and it encodes a 36-kDa protein that is essential for viability at all temperatures. Mutational analysis reveals that three dbf8 alleles are nonsense mutations affecting the carboxy-terminal third of the encoded protein. Since all of these mutations confer temperature sensitivity, it appears that the carboxyl-terminal third of the protein is essential only at a restrictive temperature. In support of this conclusion, an insertion of URA3 at the same position also confers a temperature-sensitive phenotype. Although they show no evidence of DNA damage, dbf8 mutants exhibit increased rates of chromosome loss and nondisjunction even at a permissive temperature. Taken together, our data suggest that Dbf8p plays an essential role in chromosome segregation.

ATP-Binding Cassette Transporters↗
PubMed1995

Regulation of chromosome segregation by Glc8p, a structural homolog of mammalian inhibitor 2 that functions as both an activator and an inhibitor of yeast protein phosphatase 1.

The Ipl1 protein kinase is essential for proper chromosome segregation and cell viability in the budding yeast Saccharomyces cerevisiae. We have previously shown that the temperature-sensitive growth phenotype of conditional ipl1-1ts mutants can be suppressed by a partial loss-of-function mutation in the GLC7 gene, which encodes the catalytic subunit (PP1C) of protein phosphatase 1, thus suggesting that this enzyme acts in opposition to the Ipl1 protein kinase in regulating yeast chromosome segregation. We report here that the Glc8 protein, which is related in primary sequence to mammalian inhibitor 2, also participates in this regulation. Like inhibitor 2, the Glc8 protein is heat stable, exhibits anomalous electrophoretic mobility, and functions in vitro as an inhibitor of yeast as well as rabbit skeletal muscle PP1C. Interestingly, overexpression as well as deletion of the GLC8 gene results in a partial suppression of the temperature-sensitive growth phenotype of ipl1ts mutants and also moderately reduces the amount of protein phosphatase 1 activity which is assayable in crude yeast lysates. In addition, the chromosome missegregation phenotype caused by an increase in the dosage of GLC7 is totally suppressed by the glc8-delta 101::LEU2 deletion mutation. These findings together suggest that the Glc8 protein is involved in vivo in the activation of PP1C and that when the Glc8 protein is overproduced, it may also inhibit PP1C function. Furthermore, site-directed mutagenesis studies of GLC8 suggest that Thr-118 of the Glc8 protein, which is equivalent to Thr-72 of inhibitor 2, may play a central role in the ability of this protein to activate and/or inhibit PP1C in vivo.

Amino Acid Sequence↗
PubMed1987

Replication and segregation of plasmids containing cis-acting regulatory sites of silent mating-type genes in Saccharomyces cerevisiae are controlled by the SIR genes.

In Saccharomyces cerevisiae, two cis-acting regulatory sites called E and I flank the silent mating-type gene, HMRa, and mediate SIR-dependent transcriptional repression of the a1-a2 promoters. It has been shown previously that the E and I sites have plasmid replicator (ARS) activity. We show in this report that the ARS activity of the E and I sites is governed by the SIR genotype of the cell. In wild-type cells, a plasmid carrying the E site from HMRa (HMR E) in the vector YIp5 exhibited very high mitotic stability at a copy number of approximately 25 per cell. However, in sir2, sir3, or sir4 mutants, plasmids with HMR E had the low mitotic stability characteristic of plasmids containing ARS1, a SIR-independent replicator. Elevated mitotic stability of plasmids that carry HMR E is due to a segregation mechanism provided by SIR and HMR E. In sir2 and sir4 mutants, the plasmid copy number was significantly lowered, suggesting that these gene products also participate in the replication of plasmids carrying HMR E. The phenotype of point mutations introduced at an 11-base-pair ARS consensus sequence present at HMR E indicated that this sequence is functional but not absolutely required for autonomous replication of the plasmid and that it is not required for SIR-dependent mitotic stabilization. A plasmid carrying both a centromere and HMR E exhibited reduced mitotic stability in wild-type cells. This destabilization appeared to be due to antagonism between the segregation functions provided by the centromere and by HMR E.

Base Sequence↗
PubMed1989

Genetic segregation analysis of familial mitral valve prolapse shows no linkage to fibrillar collagen genes.

Three pedigrees were identified in which mitral valve prolapse seemed to be inherited as a mendelian autosomal dominant trait. The segregation of the genes encoding the major fibrillar collagens present in valve tissue, collagens I and III, was analysed by use of restriction enzyme site variants as genetic markers. In one pedigree there was discordance between the segregation of the disease and markers for all three collagen genes. In another, there was discordance between the disease and markers for both collagen I loci. This is evidence against the disease being generally the result of mutations of the genes encoding the major fibrillar collagens.

Collagen↗
PubMed1978

Segregation of an insertional chromosome rearrangement in 3 generations.

The interstitial deletion of a segment of chromosome 13, 13q21 leads to 13q22, and its inversion and insertion into the long arm of chromosome 3 at breakpoint q12, was found to segregate in 3 generations of a family. Segregation of this 3 break rearrangement gave rise to individuals monosomic, trisomic, or balanced for the involved segment. Monosomy for 13q21 leads to 13q22 was associated with mental retardation, expressive aphasia, microcephaly, hand abnormalities, and short stature. Partially trisomic individuals had normal mentality, extremely high arched palate, and mild dysmorphic features. There was no evidence for retinoblastoma in the individuals examined. The balanced carriers were normal. Comparison of monosomic individuals with one previous report of a similar deletion reveals marked phenotypic similarities.

Adult↗
PubMed1978

Genetic studies of acute infantile spinal muscular atrophy (SMA type I). An analysis of sex ratios, segregation ratios, and sex influence.

An analysis of segregation and sex ratios, and of sex influence, was undertaken in a series of 78 index patients with acute infantile spinal muscular atrophy (SMA type I). The sex ratio of index patients was 2.0, and the excess of males was shown to occur principally among sporadic cases. The sex ratio of familial cases did not differ significantly from 1.0. The implications of this are discussed. No sex influence on age at onset, or on life expectancy, was present. The segregation ratio (Weinberg Proband method) was 0.29 for all index cases, and 0.26 for all cases excluding those referred specifically to a genetic counselling clinic. Autosomal recessivity is confirmed for this disease, with the probable inclusion of unrecognised male phenocopies in clinical series.

Acute Disease↗
PubMed1988

Structural and segregation analysis of the type II collagen gene (COL2A1) in some heritable chondrodysplasias.

Seventy-seven persons with a variety of heritable chondrodysplasias were screened for gross rearrangements of the structural gene encoding the major cartilage collagen, collagen II. None was found. Segregation of the locus (COL2A1) was studied in 19 pedigrees using three restriction site dimorphisms (shown by PvuII, HindIII, and BamHI) and a length polymorphism as linkage markers. Discordant segregation between COL2A1 and the mutant locus was seen in pedigrees with multiple epiphyseal dysplasia, autosomal recessive spondyloepiphyseal dysplasia tarda, hypochondroplasia, pseudoachondroplasia, diaphyseal aclasis, and trichorhinophalangeal syndrome. One pedigree with diastrophic dysplasia was weakly concordant. Autosomal dominant spondyloepiphyseal dysplasia tarda and metaphyseal chondrodysplasia (type Schmid) were not informative. We conclude that mutations of the collagen II gene are not a common feature of the heritable chondrodysplasias. Since the chondrocyte binding protein, chondrocalcin, is also encoded at COL2A1 our conclusions apply equally to this gene.

Calcium-Binding Proteins↗
PubMed1990

Segregation analysis of dominant osteogenesis imperfecta in Italy.

We have performed linkage analysis in seven Italian families, in which mild osteogenesis imperfecta (OI) segregated as a dominant trait, by means of six DNA restriction fragment length polymorphisms (RFLPs) of type I collagen genes. OI type I was linked to the alpha 1(I) gene (COL1A1) in two families, and to the alpha 2(I) gene (COL1A2) in one family. OI type IV segregated with COL1A2 in two families. In two OI type I families, the molecular genetic data were insufficient for exclusion of one gene. Four DNA polymorphisms were particularly informative for cosegregation analysis of OI in Italian kindreds.

Adult↗
PubMed1994

Segregation analysis of Alagille syndrome.

Alagille syndrome (AGS) is a well defined genetic disorder characterised by five major features. An autosomal dominant mode of transmission with reduced penetrance has been suggested by the analysis of a limited number of families. However there has been no statistical analysis. We report here the first segregation analysis of AGS, using 33 families collected through 43 probands. Segregation analysis of these families allowed us to conclude that AGS is transmitted as a dominant disorder with 94% penetrance and 15% of cases are sporadic. The expressivity of the phenotype was variable and 26 persons (15 parents and 11 sibs) were identified as presenting minor forms of the disease. These results are valuable for genetic counselling.

Alagille Syndrome↗
PubMed1996

Der(22)t(11;22) resulting from a paternal de novo translocation, adjacent 1 segregation, and maternal heterodisomy of chromosome 22.

The t(11;22) (q23;q11) translocation is the most frequently identified familial reciprocal translocation in humans. In translocation carriers, 3:1 meiotic segregation with tertiary trisomy can occur resulting in abnormal progeny with the der(22) as the supernumary chromosome. Affected children have a distinct phenotype with multiple anomalies and severe mental retardation. We have identified a child with developmental delay and multiple anomalies consistent with the der(22) phenotype. Cytogenetic analysis showed an abnormal chromosome complement of 47,XX,+der(22)t(11;22)(q23; q11) in all 50 cells analysed. FISH analysis using chromosome 11 and 22 painting probes showed a pattern consistent with a reciprocal translocation of the distal bands 11q23 and 22q11 respectively. Parental karyotypes were normal. RFLP analysis of locus D22S43, which maps above the t(11;22) breakpoint, showed that the der(22) was paternal in origin and indicated that the normal chromosomes 22 were the probable result of maternal heterodisomy. RFLP analysis of locus D22S94, which maps below the t(11;22) breakpoint, also suggested that both normal chromosomes 22 of the child represented the two maternal homologues. Non-paternity was excluded through the analysis of 10 microsatellite markers distributed on 10 different chromosomes and three VNTRs on three different chromosomes. To the best of our knowledge, this is the first reported case of a patient with an abnormal karyotype resulting from a de novo translocation in the paternal germline with probable unbalanced adjacent 1 segregation and maternal non-disjunction of chromosome 22 in meiosis I.

Abnormalities, Multiple↗
PubMed1996

Discordant segregation of Xq28 markers and a mutation in the L1 gene in a family with X linked hydrocephalus.

X linked recessive hydrocephalus is the most common hereditary form of hydrocephalus. Genetic analysis indicates that the majority of cases are caused by mutations in a single gene in Xq28, recently identified as the gene for neural cell adhesion molecule L1. Genetic heterogeneity for this disorder was suggested following the description of a single large pedigree where X linked hydrocephalus showed lack of linkage to Xq28 markers flanking the L1 gene. Mutation analysis in this family shows a single base pair deletion within the coding sequence of the L1 gene that would result in truncation of the mature protein. The nature of the mutation and its segregation with the disease through the pedigree indicate that it is the cause of X linked hydrocephalus in this family. These results are at odds with data obtained through segregation of alleles for markers flanking the L1 gene. Somatic and germline mosaicism is the most plausible explanation for these data, which also provide further evidence for genetic homogeneity of X linked hydrocephalus.

Base Sequence↗
PubMed1997

Neurogenic chronic idiopathic intestinal pseudo-obstruction, patent ductus arteriosus, and thrombocytopenia segregating as an X linked recessive disorder.

We present a family with three affected males in two generations with congenital neurogenic chronic idiopathic intestinal pseudo-obstruction (CIIP), patent ductus arteriosus, and large platelet thrombocytopenia apparently segregating as an X linked recessive disorder. The pattern of segregation of DNA markers within the family is consistent with linkage to the previously described neurogenic CIIP (CIIPX) locus at Xq28. This combination may represent a new contiguous gene disorder and appears to have a good prognosis with supportive therapy.

Abnormalities, Multiple↗