Biomedical subjects

L W Liao

Publications and source records attributed to L W Liao.

8 recordsLinked to original sources

PubMed1991

The development of virus-resistant alfalfa, Medicago sativa L.

We have generated more than 100 transgenic alfalfa plants, via Agrobacterium-mediated gene transfer, from genotypes selected from five alfalfa cultivars. These plants express the genes for kanamycin resistance and for the coat protein of alfalfa mosaic virus (AMV). The strongest expressers accumulated nearly 500 ng coat protein per mg soluble leaf protein. AMV inoculation of protoplasts from these strong expressers indicated that they were resistant to infection by AMV, while protoplasts from plants containing about a hundred-fold less coat protein and from control untransformed plants were not. Transgenic alfalfa plants containing large amounts of coat protein were, likewise, resistant to AMV. These plants did not develop systemic infections following inoculation with up to 50 micrograms/ml AMV, while inoculated control plants developed systemic infections following inoculation with as little as 10 micrograms/ml AMV. These results demonstrate that expression of the AMV coat protein gene confers resistance to AMV infection in transgenic alfalfa plants.

Capsid↗

PubMed1983

Target sequences for the C. elegans transposable element Tc1.

The target sequences for two independent insertions of the transposable element Tc1 from Caenorhabditis elegans show homology. Because both insertions are at palindromic TA/AT sequences, the exact boundaries of Tc1 cannot be distinguished; Tc1 could be 1610 bp and flanked by a 2-bp duplication of the target site or it could be 1612 bp and without target site duplication. The latter possibility implies a novel manner for insertion of a transposable element.

Animals↗

PubMed1983

Sequence of the C. elegans transposable element Tc1.

The complete nucleotide sequence was determined for Tc1, a transposable element in the nematode Caenorhabditis elegans. The 1610-base-pair element terminates in 54-base-pair perfect inverted repeats and is flanked by a 2-base-pair duplication of the target sequence. The Tc1 sequence contains two long open reading frames on the same DNA strand but in different translational reading frames. The positions of transcriptional control sequences suggest that a single transcript is made, which could produce two polypeptides, 273 and 112 amino acids in length. These features, i.e. terminal repeats, target site duplication and open reading frames, make Tc1 similar to transposable elements from other species.

Animals↗

PubMed1983

Analysis of a transposable element in Caenorhabditis elegans.

A transposable element, designated Tc1, has been characterized in Caenorhabditis elegans. Tc1 is 1.7 kilobases long, has an inverted terminal repeat of less than 100 base pairs, and is repeated as a highly conserved element. The copy number and genomic positions of Tc1 are extremely variable among strains, implying that Tc1 is mobile. However, progeny of interstrain crosses did not show hybrid dysgenic traits that might be due to Tc1 transposition.

Animals↗

PubMed1981

Differences among H1 histone subfractions in binding to linear and superhelical DNA. Sedimentation velocity studies.

H1 histone subfractions exhibit differential abilities in aggregating superhelical DNA, as measured by sedimentation velocity analysis. In 0.15 M NaCl, all the calf thymus H1 subfractions bound to superhelical PM2 DNA to produce nonaggregated H1-DNA complexes as well as rapidly sedimenting, aggregated complexes. Notably, the distribution of the complexes between the nonaggregated and aggregated forms was a function of ionic strength and also depended on which H1 subfraction was complexed to the superhelical DNA. All of the H1 subfractions interacted preferentially with superhelical over relaxed PM2 DNA. The cooperative binding of H1 subfractions to linear T7 DNA produced only aggregated H1-DNA complexes in 0.15 M NaCl, while leaving some DNA free. The compositional and structural variation between the subfractions of H1 histone serves as a basis for their differential effectiveness in H1-induced aggregation of superhelical DNA. The observed sensitivity of aggregation to NaCl concentration is interpreted in terms of a dependence on hydrophobic interactions, such as the proper folding of the particular H1 subfraction and intermolecular interactions between neighboring hydrophobic regions, as well as on nonspecific shielding of DNA charge. These sedimentation velocity analyses augment previous studies on the interactions of H1 subfractions with linear and superhelical DNA using circular dichroism, viscosity, and filter-binding analyses. The involvement of particular H1 and DNA conformations in producing the various types of H1-DNA interactions characterized in these studies might also apply to chromatin structure.

Animals↗

PubMed1981

Condensation of dinucleosomes by individual subfractions of H1 histone.

Dinucleosomes purified from micrococcal nuclease digests of steer kidney nuclei were stripped of H1 histone by exposure to 0.50 M NaCl. They were then formed in a complex with individual subfractions of calf thymus H1 histone by dialysis of histone-dinucleosome mixtures from 0.50 M NaCl to concentrations of NaCl between 0 M and 0.08 M; between 0.30 M and 0.10 M the complexes precipitated, and so were not included in the study. The presence of H1 in the complexes was shown to cause an asymmetrical, ordered condensation as revealed by distortions of the circular dichroic spectrum of the DNA. The distortions were negligible at 0.04 M NaCl and below, and increased as a function of ionic strength between 0.05 M and 0.08 M. The degree of distortion of the spectrum, and therefore the nature of dinucleosome condensation, differed greatly from one H1 subfraction to the next. One of the three subfractions tested had almost no effect on the circular dichroism in comparing its dinucleosome complex to H1-depleted dinucleosomes. The other subfractions to different degrees produced large distortions that resulted in spectra that were of the psi type at the higher salt concentration.

Animals↗

PubMed1981

Differences among subfractions of H1 histone in their interactions with linear and superhelical DNA. Circular dichroism.

Interactions between subfractions of ox thymus H1 histone and either linear T7 DNA or superhelical PM2 DNA were studied by measuring the circular dichroism of H1:DNA complexes. H1 subfractions differed from one to the next in their effectiveness at distorting the circular dichroic spectrum of DNA by as much as 3- to 4-fold for both forms of DNA. The order of effectiveness of the subfractions was the same at all ionic strengths between 0.05 M and 0.25 M, but the degree of spectral distortion caused by any of the subfractions was sensitive to the salt concentration. At 0 M NaCl and above 3 M NaCl, there was little or no distortion of the spectrum of DNA by any subfraction; the maximum effectiveness for all of the subfractions was at 0.15 M to 0.2 M NaCl whether the DNA was linear or superhelical. Between 0 M and 0.15 M NaCl, the H1 subfractions in free solution underwent a conformational change from a substantially unfolded state to one that is presumably the native state. This was revealed by circular dichroism. In part, this folding of the protein molecules must account for the effect of salt on the ability of H1 to distort the circular dichroism of DNA when the two macromolecules are brought together in complex formation. The distortion of the circular dichroism of DNA by H1:DNA complex formation is thought to be due to side-by-side aggregation of fibers in an asymmetrically ordered array. Apparently, the different H1 subfractions induce formation of H1:DNA complexes that differ in degree of orderliness or in a more complicated geometric parameter of the array, and this is true for superhelical as well as linear DNA.

Animals↗

PubMed1981

The amino acid sequence of residues 1-104 of CTL-1, a bovine H1 histone.

The amino acid sequence of the first 104 residues of calf thymus H1 histone subfraction (CTL-1), one of the H1 histones from bovine thymus, was determined by use of peptides derived from chymotryptic and staphylococcus protease digestion. The first 35 residues differ from the corresponding regions of a rabbit thymus H1 (RTL-3) and trout H1 by 30 and 39%, respectively, while in the region between residues 36 and 104 CTL-1 differs from the rabbit histone by only 4% and from the trout histone by only 16%. Although the differences between CTL-1 and sea urchin H1 are much greater, it is still evident that the sequence between residue 36 and residue 104 has been conserved much more than that between residues 1 and 35.

Amino Acid Sequence↗