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PubMed1994

A yeast TCP-1-like protein is required for actin function in vivo.

We previously identified the ANC2 gene in a screen for mutations that enhance the defects caused by yeast actin mutations. Here we report that ANC2 is an essential gene that encodes a member of the TCP-1 family. TCP-1-related proteins are subunits of cytosolic heteromeric protein complexes referred to as chaperonins. These complexes can bind to newly synthesized actin and tubulin in vitro and can convert these proteins into an assembly-competent state. We show that anc2-1 mutants contain abnormal and disorganized actin structures, are defective in cellular morphogenesis, and are hypersensitive to the microtubule inhibitor benomyl. Furthermore, overexpression of wild-type Anc2p ameliorates defects in actin organization and cell growth caused by actin overproduction. Mutations in BIN2 and BIN3, two other genes that encode TCP-1-like proteins, also enhance the phenotypes of actin mutants. Taken together, these findings demonstrate that TCP-1-like proteins are required for actin and tubulin function in vivo.

Actins↗
PubMed1989

Coevolution of the major histocompatibility complex and the t-complex in the mouse. I. Generation and maintenance of high complementarity associations.

A quantitative model is developed to explore the effects of prezygotic and postzygotic incompatibility on the origin and maintenance of associations between the major histocompatibility complex (MHC) and the t-complex in the mouse. Incompatibility is represented by a reduction in the rate of conception or gestation of offspring derived from sperm bearing MHC antigens in common with the mother. Incompatibility encourages the evolution of associations from a state of complete independence between the two complexes by promoting the invasion of all novel antigens, including those that exhibit associations with the t-complex. Incompatibility can modify the relative numbers of antigens associated with each haplotype by actively promoting the exclusion or invasion of recombinants that bear formerly +-specific or t-specific antigens on the alternative haplotype. The results of the analysis indicate that the state of complete independence between the MHC and the t-complex is not preserved over evolutionary time in the presence of incompatibility. Further, the expression of incompatibility maintains fully associated states that include a single antigen associated with the t-haplotype and up to three to five antigens associated with the +-haplotype within a single population.

Animals↗
PubMed1989

Coevolution of the major histocompatibility complex and the t-complex in the mouse. II. Modification of response to sharing of histocompatibility antigens.

Selective pressures imposed by high complementarity associations between the major histocompatibility complex (MHC) and the t-complex on a locus that modifies the expression of prezygotic and postzygotic incompatibility are investigated through the analysis of a quantitative model. Sharing of MHC antigens between mates or between mother and offspring elicits weak inhibition of conception or gestation. In the presence of high complementarity associations between the MHC and the t-complex, weak incompatibility depresses the mean fitness of the population. Nevertheless, natural selection favors the enhancement of the expression of incompatibility if the number of antigens associated with the +-haplotype exceeds the number associated with the t-haplotype by a sufficient margin. Under absolute linkage between the modifier locus and the t-complex, the number associated with the +-haplotype need only be greater than the number associated with the t-haplotype. In the absence of linkage, a twofold difference is sufficient to ensure the initial increase of modifier alleles that intensify the expression of incompatibility.

Alleles↗
PubMed1987

Molecular evidence for the rapid propagation of mouse t haplotypes from a single, recent, ancestral chromosome.

Mouse t haplotypes are variant forms of chromosome 17 that exist at high frequencies in worldwide populations of two species of commensal mice. To determine both the relationship of t haplotypes to each other and the species within which they exist, 35 representative t haplotypes were analyzed by means of 10 independent molecular probes, including five DNA clones and five polypeptide spots identified by means of two-dimensional gel electrophoresis. All of the tested haplotypes were found to share restriction fragments and polypeptide spots that are absent in mice carrying wild-type forms of chromosome 17. This observation provides the first direct evidence that all of the known t haplotypes are descendents of a single ancestral chromosome. The absence of variation among t haplotypes could mean that this ancestral chromosome existed relatively recently, in which case it would be necessary to postulate introgressions of t haplotypes across species lines to explain their presence in both Mus domesticus and M. musculus. Alternatively, it is possible that the ancestral chromosome existed prior to the split between M. domesticus and M. musculus and that, by chance, our probes fail to detect polymorphisms that exist among the t haplotypes. A further result of our analysis is the characterization of a partial t haplotype in a wild population of Israeli mice.

Animals↗
PubMed1988

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes.

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.

Animals↗
PubMed1995

Evolution of the chaperonin families (Hsp60, Hsp10 and Tcp-1) of proteins and the origin of eukaryotic cells.

The members of the 10 kDa and 60 kDa heat-shock chaperonin proteins (Hsp10 and Hsp60 or Cpn10 and Cpn60), which form an operon in bacteria, are present in all eubacteria and eukaryotic cell organelles such as mitochondria and chloroplasts. In archaebacteria and eukaryotic cell cytosol, no close homologues of Hsp10 or Hsp60 have been identified. However, these species (or cell compartments) contain the Tcp-1 family of proteins (distant homologues of Hsp60). Phylogenetic analysis based on global alignments of Hsp60 and Hsp10 sequences presented here provide some evidence regarding the evolution of mitochondria from a member of the alpha-subdivision of Gram-negative bacteria and chloroplasts from cyanobacterial species, respectively. This interference is strengthened by the presence of sequence signatures that are uniquely shared between Hsp60 homologues from alpha-purple bacteria and mitochondria on one hand, and the chloroplasts and cyanobacterial hsp60s on the other. Within the alpha-purple subdivision, species such as Rickettsia and Ehrlichia, which live intracellularly within eukaryotic cells, are indicated to be the closest relatives of mitochondrial homologues. In the Hsp60 evolutionary tree, rooted using the Tcp-1 homologue, the order of branching of the major groups was as follows: Gram-positive bacteria--cyanobacteria and chloroplasts--chlamydiae and spirochaetes--beta- and gamma-Gram-negative purple bacteria--alpha-purple bacteria--mitochondria. A similar branching order was observed independently in the Hsp10 tree. Multiple Hsp60 homologues, when present in a group of species, were found to be clustered together in the trees, indicating that they evolved by independent gene-duplication events. This review also considers in detail the evolutionary relationship between Hsp60 and Tcp-1 families of proteins based on two different models (viz. archaebacterial and chimeric) for the origin of eukaryotic cell nucleus. Some predictions of the chimeric model are also discussed.

Amino Acid Sequence↗
PubMed1995

The thermosome of Thermoplasma acidophilum and its relationship to the eukaryotic chaperonin TRiC.

A high molecular-mass protein complex from the archaebacterium Thermoplasma acidophilum, referred to here as the 'thermosome', is built from two subunits (M(r) 58 and 60). The thermosome has been purified to homogeneity. The molecular mass of the native complex was determined to be 1061 +/- 30 Da by scanning transmission electron microscopy. It shows a weak ATPase activity and is able to bind denatured polypeptides. Averages obtained from electron micrographs of negatively stained molecules in the end-on and side-on orientations, respectively, were compared with those of the t-complex polypeptide 1 ring complex (TRiC), isolated from bovine testes. Both molecules consist of two stacked pseudo eightfold symmetric rings which build up a cylindrical particle with a large cavity in the center. Sequence alignments of peptides generated from both subunits of the thermosome and different subunits of TRiC reveal a high partial similarity to each other and to the archaebacterial chaperonin thermophilic factor 55 from Sulfolobus shibatae as well as to eukaryotic TCP1 proteins. These striking structural similarities confirm the proposition that all these molecules belong to a single protein family which is structurally and functionally related to the GroEL class of molecular chaperones.

Adenosine Triphosphatases↗
PubMed1991

The yeast homolog to mouse Tcp-1 affects microtubule-mediated processes.

A Saccharomyces cerevisiae homolog to Drosophila melanogaster and mouse Tcp-1 encoding tailless complex polypeptide 1 (TCP1) has been identified, sequenced, and mapped. The mouse t complex has been under scrutiny for six decades because of its effects on embryogenesis and sperm differentiation and function. TCP1 is an essential gene in yeast cells and is located on chromosome 4R, linked to pet14. The TCP1-encoded proteins in yeast, Drosophila, and mouse cells share between 61 and 72% amino acid sequence identities, suggesting a primordial function for the TCP1 gene product. To assess function, we constructed a cold-impaired recessive mutation (tcp1-1) in the yeast gene. Cells carrying the tcp1-1 mutation grew linearly rather than exponentially at the restrictive temperature of 15 degrees C with a generation time of approximately 32 h in minimal medium. Both multinucleate and anucleate cells accumulated with time, suggesting that the linear growth kinetics may be explained by the generation of anucleate buds incapable of further cell division. In addition, the multinucleate and anucleate cells contained morphologically abnormal structures detected by anti-alpha-tubulin antibodies. The kinetics of appearance of these abnormalities suggest that they are a direct consequence of loss of function of the TCP1 protein and not a delayed, indirect consequence of cell death. We also observed that strains carrying tcp1-1 were hypersensitive to antimitotic compounds. Taken together, these observations imply that the TCP1 protein affects microtubule-mediated processes.

Amino Acid Sequence↗
PubMed1995

Transient and restricted expression during mouse embryogenesis of Dll1, a murine gene closely related to Drosophila Delta.

The Drosophila Delta (Dl) gene is essential for cell-cell communication regulating the determination of various cell fates during development. Dl encodes a transmembrane protein, which contains tandem arrays of epidermal-growth-factor-like repeats in the extracellular domain and directly interacts with Notch, another transmembrane protein with similar structural features, in a ligand-receptor-like manner. Similarly, cell-cell interactions involving Delta-like and Notch-like proteins are required for cell fate determinations in C. elegans. Notch homologues were also isolated from several vertebrate species, suggesting that cell-to-cell signaling mediated by Delta- and Notch-like proteins could also underlie cell fate determination during vertebrate development. However, in vertebrates, no Delta homologues have yet been described. We have isolated a novel mouse gene, Dll1 (delta-like gene 1), which maps to the mouse t-complex and whose deduced amino acid sequence strongly suggests that Dll1 represents a mammalian gene closely related to Drosophila Delta. Dll1 is transiently expressed during gastrulation and early organogenesis, and in a tissue-restricted manner in adult animals. Between day 7 and 12.5 of development, expression was detected in the paraxial mesoderm, closely correlated with somitogenesis, and in subsets of cells in the nervous system. In adult animals, transcripts were detected in lung and heart. Dll1 expression in the paraxial mesoderm and nervous system is strikingly similar to the expression of mouse Notch1 during gastrulation and early organogenesis. The overlapping expression patterns of the Dll1 and Notch1 genes suggest that cells in these tissues can communicate by interaction of the Dll1 and Notch1 proteins. Our results support the idea that Delta- and Notch-like proteins are involved in cell-to-cell communication in mammalian embryos and suggest a role for these proteins in cellular interactions underlying somitogenesis and development of the nervous system.

Amino Acid Sequence↗
PubMed1993

Incorporation of tubulin subunits into dimers requires GTP hydrolysis.

A toroid multisubunit complex of 800-900 kDa has been implicated in assisting protein folding of at least two cytoplasmic proteins, actin and tubulin. This process is dependent on the presence of magnesium ions and ATP hydrolysis. In vitro translation of cDNAs encoding different alpha- and beta-tubulin isotypes also gives rise to the formation of complexes of about 300 kDa. These complexes have been functionally implicated in the incorporation of tubulin monomers within the tubulin heterodimer. This work shows that, in addition to ATP hydrolysis, the incorporation of newly synthesized tubulin subunits into functional heterodimers requires GTP hydrolysis in the presence of magnesium ions. A two-step process is suggested, a first ATP-dependent step in which the 900 kDa complexes are implicated in a similar way to the step taking place in actin folding, and a second GTP-dependent step in which the 300 kDa complexes are involved in the assembly of the heterodimer.

Adenosine Triphosphate↗
PubMed1990

Sequence and structural homology between a mouse T-complex protein TCP-1 and the 'chaperonin' family of bacterial (GroEL, 60-65 kDa heat shock antigen) and eukaryotic proteins.

A mammalian cytoplasmic protein TCP-1, encoded by a gene within the mouse t-complex, has been found to exhibit highly significant (p much less than 0.00001) sequence homology to the 'chaperonin' family of bacterial and eukaryotic proteins (viz. groEL protein of E. coli, rubisco subunit binding protein of plant chloroplasts, yeast hsp58 and mammalian P1 proteins and 60-65 kDa mycobacterial antigen). With the introduction of few gaps, the amino acid sequence of TCP-1 shows between 60-63% similarity (17-20% identical residues and 42-45% conserved substitutions) throughout its length to various chaperonin proteins, indicating a common evolutionary origin. The sequence data also suggest that in contrast to the endosymbiotic origin of mitochondrial and chloroplast chaperonins, the cytoplasmic TCP-1 may have directly descended from the common universal ancestor via eukaryotic lineage. The observed similarity between TCP-1 and the 60-65 kDa bacterial 'common antigen' is also of importance from the viewpoint of immune/autoimmune response.

Amino Acid Sequence↗
PubMed1988

Interaction of rat testis protein, TP, with nucleosome core particle.

Circular dichroism studies have revealed that addition of testis specific protein, TP in vitro, to rat testes nucleosome core particle resulted in a decrease in the compaction of the core particle DNA. This was also corroborated by thermal denaturation analysis. Addition of TP to nucleosome core particle resulted in the conversion of a biphasic transition towards a single phase. However, at the same time there was a 20% reduction in the overall hyperchromicity of core particle DNA at core particle to TP molar ratios of 1:2 and 1:3. These observations along with our earlier report, showing the DNA melting properties of TP, suggest that TP may play an important role in the disassembly process of nucleosome core particle during spermiogenesis.

Animals↗
PubMed1987

Characterization of a cDNA clone encoding a basic protein, TP2, involved in chromatin condensation during spermiogenesis in the mouse.

A cDNA clone encoding a small cysteine and serine-rich basic protein has been isolated from a mouse testis cDNA library. This cDNA clone encodes the mouse homologue of a protein involved in the initial phases of condensation of chromatin during spermiogenesis in rats, TP2, based on similarities in the sequence of the carboxyl terminus, composition, molecular weight, and electrophoretic mobility. Mouse TP2 can be divided into a highly basic domain comprising about one-third of the polypeptide chain at the carboxyl terminus and a much less basic domain comprising the remaining two-thirds at the amino terminus. The 5' end of the mouse TP2 mRNA contains two in-phase initiation codons both of which may be used generating two polypeptides which differ in length at the amino terminus. Southern blots demonstrate that there is a single copy of the TP2 gene in the mouse genome and Northern blots demonstrate that the polyadenylated TP2 mRNA is present at high and essentially equal levels in early and late haploid cells, and that it is virtually absent from meiotic cells.

Amino Acid Sequence↗