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C Ko

Publications and source records attributed to C Ko.

54 records · Page 3Linked to original sources
PubMed1984

Isolation and sequence of the structural gene for cytochrome c oxidase subunit VI from Saccharomyces cerevisiae.

Using synthetic oligodeoxyribonucleic acid probes we have identified and isolated COX6, the structural gene for subunit VI of cytochrome c oxidase from Saccharomyces cerevisiae. The nucleotide sequence of COX6 predicts an amino acid sequence, for the mature subunit VI polypeptide, which is in perfect agreement with that determined previously. The nucleotide sequence of COX6 also predicts that subunit VI is derived from a precursor with a highly basic 40-amino acid NH2-terminal presequence. This precursor has been observed after in vitro translations programmed by yeast poly(A+)RNA. Northern blot analysis of poly(A+) RNA from strain D273-10B reveals that COX6 is homologous to three RNAs of 1800, 900, and 700 bases in length. By means of Southern blot analysis, the cloned gene was shown to be co-linear with yeast chromosomal DNA and to exist in a single copy in the yeast genome. An additional open reading frame, consisting of 82 codons, terminates 22 codons upstream from COX6. It is "in frame" with the COX6 coding region.

Amino Acid Sequence↗
PubMed1984

Mitochondrial membrane biogenesis: characterization and use of pet mutants to clone the nuclear gene coding for subunit V of yeast cytochrome c oxidase.

A nuclear pet mutant of Saccharomyces cerevisiae that is defective in the structural gene for subunit V of cytochrome c oxidase has been identified and used to clone the subunit V gene (COX5) by complementation. This mutant, E4-238 [24], and its revertant, JM110, produce variant forms of subunit V. In comparison to the wild-type polypeptide (Mr = 12,500), the polypeptides from E4-238 and JM110 have apparent molecular weights of 9,500 and 13,500, respectively. These mutations directly alter the subunit V structural gene rather than a gene required for posttranslational processing or modification of subunit V because they are cis-acting in diploid cells; that is, both parental forms of subunit V are produced in heteroallelic diploids formed from crosses between the mutant, revertant, and wild type. Several plasmids containing the COX5 gene were isolated by transformation of JM28, a derivative of E4-238, with DNA from a yeast nuclear DNA library in the vector YEp13. One plasmid, YEp13-511, with a DNA insert of 4.8 kilobases, was characterized in detail. It restores respiratory competency and cytochrome oxidase activity in JM28, encodes a new form of subunit V that is functionally assembled into mitochondria, and is capable of selecting mRNA for subunit V. The availability of mutants altered in the structural gene for subunit V (COX5) and of the COX5 gene on a plasmid, together with the demonstration that plasmid-encoded subunit V is able to assemble into a functional holocytochrome c oxidase, enables molecular genetic studies of subunit V assembly into mitochondria and holocytochrome c oxidase.

Cloning, Molecular↗
PubMed1983

Nuclear genes for mitochondrial proteins. Identification and isolation of a structural gene for subunit V of yeast cytochrome c oxidase.

The gene for yeast cytochrome c oxidase subunit V, COX5, has been isolated from a Saccharomyces cerevisiae DNA library by complementation of a cytochrome c oxidase subunit V mutant, JM28. One complementing plasmid, YEp13-511, with a DNA insert of 4.8 kilobase pairs, has been characterized in detail. This plasmid restores respiratory competency in JM28, results in increased cytochrome c oxidase activity and a new form of subunit V in JM28 mitochondria, and is capable of selecting mRNA for subunit V. These results indicate that YEp13-511 carries the COX5 gene and that the subunit V encoded by this plasmid gene is capable of entering the mitochondrion and assembling into a functional holocytochrome c oxidase.

Base Sequence↗
PubMed1981

Distribution of proteins between nucleus and cytoplasm of Amoeba proteus.

By transplanting nuclei between labeled and unlabeled cells, we determined the localization of the major proteins of amebas and described certain features of their intracellular distributon. We identified approximately 130 cellular proteins by fluorography of one-dimensional polyacrylamide electrophoretic gels and found that slightly less than half of them (designated NP, for nuclear proteins) are almost exclusively nuclear. About 95 percent of the other proteins (designated CP for cytoplamsic proteins) are roughly equally concentrated in nucleus and cytoplasm, but-because the cytoplasm is 50 times larger than the nucleus-about 98 percent of each of the latter is in the cytoplasm. Of the CP, roughly 5 percent are not detectable in the nucleus. Assuming that these are restricted to the cytoplasm only because, for example, they are in structures too large to enter the nucleus and labeled CP readily exit a nucleus introduced into unlabeled cytoplasm, we conclude that the nuclear envelope does not limit the movement of any nonstructural cellular protein in either direction between the two compartments. Some NP are not found in the cytoplasm (although ostensibly synthesized there) presumably because of preferential binding within the nucleus. Almost one half of the protein mass in nuclei in vivo is CP and apparently only proteins of that group are lost from nuclei when cells are lysed. Thus, while an extracellular environment allows CP to exit isolated nuclei, the nuclear binding affinities for NP are retained. Further examination of NP distribution shows that many NP species are, in fact, detectable in the cytoplasm (although at only about 1/300 the nuclear concentration), apparently because the nuclear affinity is relatively low. These proteins are electrophoretically distinguishable from the high-affinity NP not found in the cytoplasm. New experiments show that an earlier suggestion that the nuclear transplantation operation causes an artifactual release of NP to the cytoplasm is largely incorrect. Moreover, we show that cytoplasmic "contamination" of nuclear preparations is not a factor in classifying proteins by these nuclear transplantation experiments. We speculate the no mechanism has evolved to confine most CP to the cytoplasm (where they presumably function exclusively) because the cytoplasm's large volume ensures that CP will be abundant there. Extending Bonner's idea of "quasi-functional nuclear binding sites" for NP, we suggest that a subset of NP usually have a low affinity for available intranuclear sites because their main function(s) occurs at other intranuclear sites to which they bind tightly only when particular metabolic conditions demand. The other NP (those completely absent from cytoplasm) presumable always are bound with high affinity at their primary functional sites.

Amoeba↗
PubMed1978

Identification of the small nuclear RNAs associated with the mitotic chromosomes of Amoeba proteus.

Amebas contain 7 electrophoretically distinct species of small nuclear RNAs (snRNAs), some of which are known to associate in a striking manner with mitotic chromosomes. These RNAs can be divided into 2 classes, one consisting of 4 snRNA species that shuttle in a non-random way between nucleus and cytoplasm during interphase and one consisting of 3 snRNA species that do not leave the nucleus at all during interphase. In the work reported here we sought to determine which class is associated with mitotic chromosomes. Through a series of micromanipulative procedures we arranged for the shuttling snRNAs to be the only radioactive molecules in the cell. Such cells were allowed to enter mitosis, whereupon they were fixed and subjected to autoradiography. In those cells no radioactive snRNAs were found associated with mitotic chromosomes. It is concluded, therefore, that those snRNAs that do associate with mitotic chromosomes must be one or more of the non-shuttling species.--In the Discussion, how the non-shuttling snRNAs may function in cell activities is considered.

Amoeba↗
PubMed1978

Differences between nucleus and cytoplasm in the degree of actin polymerization.

For purposes of studying the degree of polymerization of actin in nuclei, nuclei from 35S-labeled amoebas (Amoeba proteus) were transplanted into unlabeled cells, which were immediately lysed and extracted under conditions considered to stabilize preexisting fibrous actin. The enucleated 35S-donor cells were similarly treated for analysis of cytoplasmic actin. The extraction conditions permitted separation of soluble (unpolymerized or G) actin from pelletable (polymerized or F) actin, and the radioactivity of each was determined after the actin was separated from other proteins by polyacrylamide gel electrophoresis. We found that about 2/3 of the actin within the nucleus is pelletable, whereas only about 1/3 of the cytoplasmic actin is pelletable. We speculate that polymerized actin in the nucleus is involved in the condensation of chromatin.

Actins↗
PubMed1978

Small nuclear RNAs: an association with condensed chromatin in amoebae.

For the purpose of studying the relationship of small nuclear RNAs (snRNAs) to chromatin, we studied the effect of the chromatin-binding agent actinomycin D (AMD) on the nuclei of amoebae. By electron microscopy we noted that when mitotic cells were placed in AMD their chromatin was highly condensed 3 h later. This contrasts strikingly with the situation in untreated cells, in which the chromatin at the same time is largely decondensed. After arranging, by nuclear transplantation of labelled nuclei into unlabelled cytoplasm, for the only labelled molecules in the cell to be 3H-snRNAs, we noted that in such cells similarly treated with AMD the labelled material was clustered in a form quite similar to that of the chromatin in 3-h post-division, AMD-treated cells. In untreated cells the 3H-snRNAs were distributed essentially uniformly throughout the nucleus. These observations, together with earlier findings that snRNAs associate with chromosomes during mitosis, lead us to conclude that snRNAs have a particular affinity for condensed chromatin.

Amoeba↗
PubMed1977

Nuclear actin: an apparent association with condensed chromatin.

In Amoeba proteus the concentration of actin is the same in the nucleus and cytoplasm. Certain characteristics, e.g., the ready loss of actin from isolated nuclei, suggest that the association with nuclei is normally not a tight one. Here we report, however, that when nuclei are isolated several hours after mitotic amebas are placed in actinomycin D (which allows normal progression of mitosis), the nuclei retain substantial amounts of actin. Since this finding correlates with other observations that the chromatin of such cells is extensively condensed, we suggest that a relationship may exist between actin and chromatin condensation.

Actins↗
PubMed1977

Small nuclear RNA localization during mitosis. An electron microscope study.

The localization of small nuclear ribonucleic acids (snRNAs) during mitosis in Amoeba proteus was studied by high voltage (1,000 kV) electron microscope autoradiography. By suitable micromanipulations, the snRNA's, labeled with [3H]uridine, were made to be the only radioactive molecules in the cell and thus easy to follow autoradiographically. During interphase the snRNA label, which is almost exclusively nuclear, is distributed fairly uniformly through the nucleus with a slightly higher amount of label over chromatin than over nonchromatin areas. During prophase the snRNAs, which continue to be largely nuclear, become highly concentrated in the condensing chromosomes. At metapase, almost all of the snRNAs are cytoplasmic and essentially none are associated with the maximally condensed chromatin. Beginning in early anaphase, the snRNAs resume their association with the chromosomes, with the degree of association increasing throughout anaphase. Most of the snRNAs are back in the nuclei by telophase, but the intranuclear localization is hard to determine. We conclude that snRNAs have a great affinity for the partially condensed chromosomes of prophase and anaphase, but none for the maximally condensed chromosomes of metaphase. A minor amount of snRNA localizations in association with nucleoli and the nuclear envelope are also reported. On the basis of these findings a role of snRNAs in genetic "reprogramming" or chromosome organization is proposed.

Amoeba↗
PubMedDate not supplied

Asian Indian women: knowledge, attitudes and behaviors toward breast cancer early detection.

Education programs have been developed to promote adherence to recommended breast cancer screening guidelines. Few studies have assessed the degree to which ethnic subgroups are perceiving and acting on the proffered information. Such assessment is vital to the creation of efficient public health interventions. This paper describes the reported breast cancer knowledge, attitudes, and screening behaviors of 194 American Asian Indian women. While monthly breast self exam adherence was low, only 40.7%, 61.3% of women 40 and older, and 70% of women 50 and older, reported having had a mammogram within the past 12 months. These rates for annual mammography screening are high relative to many other ethnic groups. While the results are encouraging, the respondents may not be representative of all Asian Indian women. The majority of these women reported that their breast cancer knowledge is inadequate. They were willing to be called upon to share with others any knowledge they gained. There is a clear opportunity for public health nurses to provide Asian Indian women with a more comprehensive understanding of breast health and disease. Those women can then share their health knowledge with other women within their ethnic group.

Adult↗