Biomedical subjects

Y Xiong

Publications and source records attributed to Y Xiong.

15 recordsLinked to original sources

PubMed1992

D type cyclins associate with multiple protein kinases and the DNA replication and repair factor PCNA.

Human cyclin D1 has been associated with a wide variety of proliferative diseases but its biochemical role is unknown. In diploid fibroblasts we find that cyclin D1 is complexed with many other cellular proteins. Among them are protein kinase catalytic subunits CDK2, CDK4 (previously called PSK-J3), and CDK5 (also called PSSALRE). In addition, polypeptides of 21 kd and 36 kd are identified in association with cyclin D1. We show that the 36 kd protein is the proliferating cell nuclear antigen, PCNA. Cyclin D3 also associates with multiple protein kinases, p21 and PCNA. It is proposed that there exists a quaternary complex of D cyclin, CDK, PCNA, and p21 and that many combinatorial variations (cyclin D1, D3, CDK2, 4, and 5) may assemble in vivo. These findings link a human putative G1 cyclin that is associated with oncogenesis with a well-characterized DNA replication and repair factor.

Amino Acid Sequence↗

PubMed1992

Growth-regulated expression of D-type cyclin genes in human diploid fibroblasts.

The human CCND1 cyclin D1/PRAD1 gene was previously identified by a genetic screen for G1 cyclin function in Saccharomyces cerevisiae and also was identified as the putative BCL1 oncogene. However, its role in human cell proliferation is not known. To determine if expression of human D-type cyclin genes correlates with the state of cell growth, we examined the level of mRNAs for CCND1 and a related gene, CCND3, in normal human diploid fibroblasts (HDF). The levels of both mRNAs decrease upon serum depletion or at high cell densities. Following stimulation of quiescent fibroblasts with serum, the mRNA levels increase gradually to a peak at about 12 hr, prior to the onset of S phase. Induction of cyclin gene expression by serum is reduced concomitantly with the decline in FOS induction in aging HDFs, suggesting a possible relationship to the decrease in the proliferative response to mitogens during cellular senescence. Cycloheximide partially blocks the induction of CCND1 and CCND3 gene expression by serum, suggesting that both de novo protein synthesis-dependent and -independent pathways contribute to induction. Treatment of HDFs with defined growth factors suggests a correlation between CCND mRNA induction and DNA synthesis. However, induction of these genes is not sufficient for the transition from quiescence through G1 into S phase.

Blood↗

PubMed1992

Molecular cloning and chromosomal mapping of CCND genes encoding human D-type cyclins.

A human D-type cyclin gene (CCND1/cyclin D1/PRAD1) was previously isolated by virtue of its ability to complement a triple G1 cyclin (Cln) deficiency of Saccharomyces cerevisiae and was also identified as a candidate BCL1 oncogene. We now report the molecular cloning of two additional human D-type cyclin genes, CCND2 (cyclin D2) and CCND3 (cyclin D3). All three human D-type cyclin genes encode small (33-34 kDa) proteins that share an average of 57% identity over the entire coding region and 78% in the cyclin box. The D-type cyclins are most closely related to cyclin A (39% identity) and cyclin E (36%), followed by cyclin B (29%) and cyclin C (21%). Isolation and characterization of genomic clones revealed two pseudogenes corresponding to CCND2 and CCND3, respectively. All three cyclin D genes are interrupted by an intron at the same position. CCND2 has been mapped to chromosome 12p13, and CCND3 has been mapped to chromosome 6p21.

Amino Acid Sequence↗

PubMed1991

Human D-type cyclin.

A cDNA library prepared from a human glioblastoma cell line has been introduced into a budding yeast strain that lacks CLN1 and CLN2 and is conditionally deficient for CLN3 function. We rescued a gene that we call cyclin D1. It is related to A-, B-, and CLN-type cyclins, but appears to define a new subclass within the cyclin gene family. Transcription of the cyclin D1 gene gives rise to two major transcripts through alternative polyadenylation. The cyclin D1 gene transcript and its 34 kd product are both abundant in the glioblastoma cell line of origin.

Amino Acid Sequence↗

PubMed1991

Inhibition of mitochondrial respiratory function by an organic solvent extractable component from an extract of burn eschar.

Saline extracts of burn eschar (CEBE) and normal skin (CENS) caused inhibition to mitochondrial respiration and inner membrane function. Ethyl acetate extracts from CEBE (D1) and CENS (D'1) caused depression of the Respiratory Control Ratio, (RCR), an inhibition of respiration rate in state 3 and stimulation to state 4 respiration. Excellent linear correlations exist between the degree of inhibition to state 3, rate of stimulation to state 4 respiration and the logarithm of doses of D1 and D'1. The effective dose ranges (0.75-0.25 mg/ml for D1 and 4-1 mg/ml for D'1) differ by one order of magnitude. The activity of NADH dehydrogenase and succinate dehydrogenase of mitochondria after incubation with the highest toxic dose of D1 or D'1 remained normal. Dinitrophenol (DNP)-stimulated respiration was moderately inhibited by D1 and D'1. No change of oligomycin-sensitive ATPase activity was demonstrated. Exogenous malondialdehyde (MDA) did not show any inhibitory effect. Preliminary studies show that D1 contains a family of free fatty acids (FFA). Incubation of normal mitochondria with D1 increased the content of saturated FFA and a decrease of unsaturated FFA. The role of other peroxidative products is under investigation.

Adenosine Triphosphatases↗

PubMed1991

Density of steam-flaked sorghum grain, roughage level, and feeding regimen for feedlot steers.

Two hundred fifty-two steers (366 kg) were assigned to a 3 x 2 x 2 factorial arrangement of three densities of steam-flaked sorghum grain (bulk [flake] density of 437, 360, and 283 g/liter, B34, B28, and B22, respectively), two roughage levels (9 [R9] and 18% [R18]) and two feeding strategies (ad libitum [AD] or multiple of maintenance [MM], 2.3, 2.5, and 2.7 MM for wk 1, 2, and 3, and 2.9 MM thereafter). Steers fed R18-AD gained faster than steers fed R18-MM (1.59 vs 1.52 kg/d, P = .10); for R9 diets, no difference (P greater than .25) was found between steers fed AD and MM (interaction, P = .07). Flake density did not affect ADG (1.53 kg, P greater than .2). Dry matter intake decreased (9.8, 9.3, and 9.0 kg/d, linear, P less than .001) and gain efficiency (G/DMI, kg of gain/100 kg of DMI) increased (15.7, 16.5, and 16.9, linear, P less than .001; quadratic, P = .19) as processing degree increased (B34 to B22). Percentage of choice carcasses for B34 (67.0%) was higher (linear, P = .05) than for B28 (51.9%) and B22 (52.3%). Fecal starch and pH were 10.8, 5.7, and 4.0%, and 6.11, 6.23, and 6.37 for B34, B28, and B22, respectively (linear, P less than .001). The correlation between fecal starch and pH was -.51 (P less than .001, n = 252). Enzymatic glucose release, in vitro 6-h gas production, microbial protein synthesis, and protein degradability were 375, 483, and 559 mg/g; 24.7, 28.2, and 31.1 ml/.2 g; 6.15, 6.88, and 7.84 g/100g; and 61.4, 56.6, and 42.2% for B34, B28, and B22, respectively (linear, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗

PubMed1990

Type I (R1) and type II (R2) ribosomal DNA insertions of Drosophila melanogaster are retrotransposable elements closely related to those of Bombyx mori.

Approximately 50% of the ribosomal DNA (rDNA) units of Drosophila melanogaster are inactivated by two different 28 S RNA ribosomal gene insertions (type I and type II). We present here the nucleotide sequence of complete type I and type II elements. Conceptual translation of these sequences revealed open reading frames (ORFs) encoding amino acid residues conserved in all retrotransposable elements. Full-length type I elements are 5.35 x 10(3) base-pairs in length and contain two overlapping ORFs. The smaller ORF (471 amino acid residues) has similarity to gag genes, while the larger ORF (1021 residues) has similarity to pol genes. Full-length type II elements are 3.6 x 10(3) base-pairs and contain one large ORF (1056 residues) that appears to represent a gag-pol fusion. Type I and type II elements are similar in structure, in the proteins they encode, and in insertion specificity to the R1Bm and R2Bm retrotransposable elements of Bombyx mori. We suggest that the D. melanogaster elements be called R1Dm and R2Dm, to reflect their structure as retrotransposons. Comparison of the R1 and R2 elements from these two widely different species revealed regions of the ORF that are likely to play an important role in the propagation of the elements. Four distinct regions of sequence conservation separated by regions of little or no sequence similarity were detected for both the R1 and R2 elements: (1) cysteine motifs of the gag gene, with three such motifs for R1 and one motif for R2; (2) a reverse transcriptase domain; (3) an integrase domain located carboxyl terminal to the reverse transcriptase region; and (4) a small region amino terminal to the reverse transcriptase domain, whose function is not known. The level of identity of the amino acid residues for these segments is 28 to 34% between the R1 elements, and 34 to 39% for the R2 elements. Finally, it may be predicted that the mechanism of unequal crossover might eventually eliminate R1 and R2 from the rDNA locus. The long history of selection at the protein level exhibited by these elements indicates that it is their active transposition that maintains them in the locus. The high level of sequence homogeneity between copies of each element within the same species is consistent with the high turnover rate expected to result from these processes.

Amino Acid Sequence↗

PubMed1990

Origin and evolution of retroelements based upon their reverse transcriptase sequences.

To study the evolutionary relationship of reverse transcriptase (RT) containing genetic elements, a phylogenetic tree of 82 retroelements from animals, plants, protozoans and bacteria was constructed. The tree was based on seven amino acid domains totalling 178 residues identified in all RTs. We have also identified these seven domains in the RNA-directed RNA polymerases from various plus-strand RNA viruses. The sequence similarity of these RNA polymerases to RT suggests that these two enzymes evolved from a common ancestor, and thus RNA polymerase can be used as an outgroup to root the RT tree. A comparison of the genetic organization of the various RT containing elements and their position on the tree allows several inferences concerning the origin and evolution of these elements. The most probable ancestor of current retroelements was a retrotransposable element with both gag-like and pol-like genes. On one major branch of the tree, organelle and bacterial sequences (e.g. group II introns and bacterial msDNA) appear to have captured the RT sequences from retrotransposons which lack long terminal repeats (LTRs). On the other major branch, acquisition of LTRs gave rise to two distinct groups of LTR retrotransposons and three groups of viruses: retroviruses, hepadnaviruses and caulimoviruses.

Amino Acid Sequence↗

PubMed1990

Improved enzymatic method to measure processing effects and starch availability in sorghum grain.

A modified enzymatic method to measure processing effects and starch availability in steam-flaked sorghum grain (SFSG) was developed. To establish the method, experiments were conducted to determine the required enzyme concentration, color reagents, precipitants, sample particle size, shaking frequency and buffer pH. Glucose release at different incubation times (0 to 48 h) from uncooked (UNC) or fully cooked (CK, 100% gelatinized) ground sorghum grain, a 50:50 mixture of UNC and CK (C50) and SFSG was determined. Glucose release from UNC, CK and SFSG was expressed as one-component equations with rate constant k and r2 of .119 and .98, 1.781 and .98, and .368 and .99, respectively; C50 was characterized by having two starch components, one with a fast rate constant, 2.624/h, and one with a slow rate constant, .066/h (R2 = .99). Different degrees of gelatinization were obtained by mixing different proportions of CK and UNC. Glucose release from these samples was highly correlated with starch gelatinization (r2 = .99). By adjusting the tension between mill rollers, five SFSG samples with bulk densities ranging from 476 to 283 g/liter (37 to 22 lb/bu) were produced; respective roller mill electrical load ranged from 21 to 51.5 amps. Enzymatic determination of glucose release resulted in values of 422, 512, 588, 618 and 678 mg/g, which were more closely related to bulk density than birefringence measurements. The modified method for starch availability determination was found to be relatively simple, fast and sensitive, and is recommended.

Animal Feed↗

PubMed1990

Estimating starch availability and protein degradation of steam-flaked and reconstituted sorghum grain through a gas production technique.

Five steam-flaked sorghum grain (SFSG) samples with bulk densities of 476, 412, 347, 309 and 283 g/liter made by adjusting tension between mill rollers and three reconstituted sorghum grain (RSG) samples with reconstitution times of 10, 20 and 30 d and a control sample were analyzed for gas production kinetics (rumen liquor fermentation) and enzymatic glucose release (amyloglucosidase). Protein degradation was estimated from 6-h gas production and residual ammonia in the liquid. Gas production followed first-order kinetics (r2 greater than .98; P less than .01) and was used to describe rate and extent of digestion kinetics. Rate of gas production increased as processing degree increased. The magnitude of increase in gas production, however, was much less for RSG than for SFSG. Linear relationships were observed between enzymatic glucose release and the gas production rate constant k as well as gas production at 4,6 and 8 h (r2 greater than .98; P less than .01). Protein degradation decreased with processing degree of SFSG but increased with reconstitution time. A technique based on 6-h gas production and residual ammonia in the liquid is proposed to estimate both ruminal starch availability and ruminal protein degradability for processed sorghum grain.

Animal Feed↗

PubMed1990

[Mosquito-net spraying with deltamethrin for malaria control].

Mosquito-nets were sprayed with 9.6mg deltamethrin per square meter for control of malaria vectors in Yibin County, Sichuan Province in 1986. In the study area, the relative population indices of Anopheles anthropophagus and An. sinensis in 35 mosquito-nets were 0.6 and 1.4 respectively; the man biting rates of these two vectors dropped by 97.8 and 90.8% respectively. The residual toxic effect of sprayed mosquito-nets, up to 104 days after spray, caused a mortality of 93.1-100% of An. anthropophagus and 87.1-100% of An. sinensis. The multiparous mosquito rate dropped by 48.4 and 51.3%. Indoor-intruding An. anthropophagus and An. sinensis were reduced by 76% and 78.3% respectively. The incidence of malaria decreased by 94.4%, the positive rate in school children declined by 77.5%. Both entomological and epidemiological indices indicated that mosquito-nets sprayed with deltamethrin could effectively control the malaria prevalence. This measure is economical and practical for control of malaria.

Animals↗

PubMed1988

Ribosomal DNA insertion elements R1Bm and R2Bm can transpose in a sequence specific manner to locations outside the 28S genes.

A fraction of the ribosomal 28S genes in some insects are interrupted at specific sites by insertion elements R1 and R2 (also called Type I and II). These elements contain long open-reading frames with homology to reverse transcriptase. We have identified in the silkmoth, Bombyx mori, copies of these elements which have inserted into sites outside the ribosomal DNA (rDNA) units. The 3' ends of all "non-rDNA" elements are identical to the elements within the 28S genes; however their 5' ends are often truncated. Each non-rDNA copy has inserted into sequences that exhibit similarity to their target sites in the 28S gene. We also demonstrate by genomic blot analysis of different strains of B. mori that insertions of R1 and R2 outside the rDNA units have been infrequent, while considerable turnover of elements has occurred within the rDNA locus. One race of B. mori has lost all copies of R1 from its rDNA units, while retaining normal levels of R2. The level of both R1 and R2 have significantly increased in a tissue culture line. These findings add considerable support to the model that R1 and R2 are retrotransposable elements that utilize sequence specific endonucleases in their integration into the genome.

Animals↗

PubMed1988

Similarity of reverse transcriptase-like sequences of viruses, transposable elements, and mitochondrial introns.

Sequences similar to reverse transcriptase (RT) of retroviruses have been found in certain DNA viruses, mitochondrial intron sequences, and a wide variety of transposable elements. While total amino acid similarity between these diverse elements is quite low, we have identified seven regions, consisting of 182 amino acids, that are common to all elements. Highly conserved residues identified in each of these regions are diagnostic for the identification and alignment of these and for future RT-like sequences. Using both the neighbor-joining and the unweighted-pair-group methods, we have derived a probable phylogenetic tree for all RT-containing elements. These elements can be divided into two major groups. Retroviruses and DNA viruses whose propagation involves an RNA intermediate are grouped with a series of transposable elements containing long terminal repeats (LTRs). The second group is made up of RT-containing sequences of fungal mitochondrial introns and a series of transposable elements that lack LTRs. The transposable elements, copia and Ty, were found to be the most difficult to position on the phylogenetic tree, as a result of their higher rate of sequence divergence. The data are most consistent with their being distant members of the LTR group (retroviruses/LTR retrotransposons).

Amino Acid Sequence↗

PubMed1988

The site-specific ribosomal DNA insertion element R1Bm belongs to a class of non-long-terminal-repeat retrotransposons.

Two types of insertion elements, R1 and R2 (previously called type I and type II), are known to interrupt the 28S ribosomal genes of several insect species. In the silkmoth, Bombyx mori, each element occupies approximately 10% of the estimated 240 ribosomal DNA units, while at most only a few copies are located outside the ribosomal DNA units. We present here the complete nucleotide sequence of an R1 insertion from B. mori (R1Bm). This 5.1-kilobase element contains two overlapping open reading frames (ORFs) which together occupy 88% of its length. ORF1 is 461 amino acids in length and exhibits characteristics of retroviral gag genes. ORF2 is 1,051 amino acids in length and contains homology to reverse transcriptase-like enzymes. The analysis of 3' and 5' ends of independent isolates from the ribosomal locus supports the suggestion that R1 is still functioning as a transposable element. The precise location of the element within the genome implies that its transposition must occur with remarkable insertion sequence specificity. Comparison of the deduced amino acid sequences from six retrotransposons, R1 and R2 of B. mori, I factor and F element of Drosophila melanogaster, L1 of Mus domesticus, and Ingi of Trypanosoma brucei, reveals a relatively high level of sequence homology in the reverse transcriptase region. Like R1, these elements lack long terminal repeats. We have therefore named this class of related elements the non-long-terminal-repeat (non-LTR) retrotransposons.

Amino Acid Sequence↗

PubMed1985

Mutational analysis of the Klebsiella pneumoniae nitrogenase promoter: sequences essential for positive control by nifA and ntrC (glnG) products.

ntr (nitrogen regulated) and nif (nitrogen fixation) promoters are structurally similar to each other but bear no resemblance to canonic Escherichia coli promoters. ntr promoters are normally activated by the ntrC (glnG) product, but they can also be activated by the ntrC-related Klebsiella pneumoniae nifA product. In contrast, nif promoters of K. pneumoniae such as the nitrogenase (nifH) promoter can only be nifA activated. In this paper, we report the isolation and characterization of 28 mutants of the K. pneumoniae nifH promoter. Class A mutants no longer respond to nifA-mediated transcription, and class B mutants can now respond to ntrC-mediated activation. These two classes of mutants define sequences important to nifA- and ntrC-mediated transcription. Most surprising is that a single base change is sufficient to convert a nifA-activated promoter into an ntrC-activated one.

Base Sequence↗