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R I Ma

Publications and source records attributed to R I Ma.

11 recordsLinked to original sources
PubMed1996

Analysis of the human gene encoding latent transforming growth factor-beta-binding protein-2.

Transforming growth factor (TGF)-beta is secreted as an inactive complex, which frequently contains a large molecular weight binding protein designated latent TGF-beta-binding protein (LTBP). Recently, the LTBPs have been shown to be a gene family that contains three known members and exhibits a multidomain structure containing cysteine-rich motifs that are also found in the fibrillin gene family. The present work seeks to characterize the gene encoding LTBP-2 and to compare its features to that of the other LTBPs and to the fibrillins. Human fibroblast libraries were used to isolate cDNA encoding LTBP-2 which was then used to identify LTBP-2 transcripts and to isolate the corresponding LTBP-2 gene. The cloned cDNA encodes a 195 kDa protein containing 20 epidermal growth factor (EGF)-like repeats, three repeats containing eight cysteines, and one segment that appears to be a hybrid of the two. Single exons encode EGF repeats while the eight-cysteine repeats are encoded in two exons. Northern analysis identified two transcripts of 7.5 and 9.0 kb, with the presently analyzed cDNA probably corresponding to the 7.5 transcript. Phylogenetic sequence comparisons demonstrated that LTBP-3 is more similar to LTBP-1 than LTBP-2, while LTBP-2 shows the most similarity to the fibrillins. These analyses suggest that LTBP-1 diverged from LTBP-3, and that LTBP-2 diverged from LTBP-1. Within the fibrillin family, fibrillin-1 is nearest to the LTBPs. While the domain structure of LTBP-2 is similar to that of the other LTBPs, LTBP-2 possesses unique regions that make it the largest member of the LTBP family. LTBP-2 may have dual functions as a member of the TGF-beta latent complex and as a structural component of microfibrils.

Adaptor Proteins, Signal Transducing↗
PubMed1995

Molecular cloning of the microfibrillar protein MFAP3 and assignment of the gene to human chromosome 5q32-q33.2.

Microfibrils having a diameter of 10-12 nm, found either in association with elastin or independently, are an important component of the extracellular matrix of many tissues, but characterization of these microfibrils is incomplete. To further our understanding of the gene structure of proteins composing the microfibrils and to identify their chromosomal location, we have cloned and characterized another microfibril protein, designated microfibril-associated protein-3 (MFAP3). The human gene encoding MFAP3 has a very simple structure, containing only two translated exons encoding a protein of 362 amino acids. Monospecific antibodies prepared against the recombinantly expressed protein reacted with the microfibrils found in ocular zonules. MFAP3 does not appear to share homology with any other known protein. The gene was found to be located on chromosome 5q32-q33.2, near the locus 5q21-q31 reported for the fibrillin gene, FBN2, which has been linked to congenital contractural arachnodactyly. MFAP3 is a candidate gene for heritable diseases affecting microfibrils.

Amino Acid Sequence↗
PubMed1986

Three-arm nucleic acid junctions are flexible.

Nucleic acid junctions are stable analogs of branched DNA structures which occur transiently in living systems. We show here that junctions which contain three double helical arms can be enzymatically oligomerized, using conventional sticky-ended ligation procedures, to create larger complexes. The products consist of a series of linked junctions separated by 20 base pairs. Junction dimers are formed that have free termini only, whereas trimers and larger species are found to be both unclosed and cyclized. The formation of a series of macrocyclic products which, surprisingly, begins with trimers and tetramers indicates that this junction is flexible about a bending axis, and perhaps twist-wise as well. We have obtained the same results from three different 3-arm junctions, two in which the junction is flanked by a 3 Watson-Crick base pairs, and one in which a G-G base pair flanks the junction.

Base Composition↗
PubMed1985

Physical characterization of a nucleic acid junction.

Normally unstable transient states of DNA, in which the linear duplex branches to form junctions with three or more arms, can be studied at the oligonucleotide level if their sequences are carefully selected. We have designed a series of oligonucleotide complexes with sequences that are restricted to prevent any major overlap among the arms, and chosen to exhibit high equilibrium stabilities, as well. The electrophoretic mobility of these complexes on polyacrylamide gels permits us to demonstrate formation of a stable four-strand complex with 1:1:1:1 stoichiometry. We review here the evidence for formation of a stable stoichiometric junction, and present new circular dichroism data showing that the arms remain in B helix geometry within the complex, and that no significant loss of structure occurs on forming a junction.

Circular Dichroism↗
PubMed1983

Fourth rank immobile nucleic acid junctions.

An immobile nucleic acid junction composed of four dodecanucleotides has been designed according to principles of minimum symmetry aided by equilibrium calculations, and has been synthesized by automated phosphotriester techniques. We can demonstrate its tetrameric character and its 1:1:1:1 stoichiometry by gel electrophoresis. Thermal denaturation monitored by ultraviolet hyperchromism indicates that the complex is stable relative to its component arms. High resolution NMR spectroscopy suggests that this junction exists in more than one conformer at room temperature. The data from this junction are compared with the data from a similar junction composed of four hexadecanucleotides.

Base Sequence↗
PubMed1981

Frameshift mutagenesis of 9-aminoacridine derivatives in Salmonella typhimurium.

It has been noted that 9-aminoacridine reverts a his C frameshift but not one in his D in the Salmonella strains used in the Ames test, without metabolic activation. The 2 sites differ in the arrangement of G and C residues present. We show here that a series of 9-aminoacridine derivatives exhibits the same selectivity as 9-aminoacridine provided there is at least one exocyclic amino hydrogen at the central ring position in acridines, or the analogous site in aminoquinolines. The results are consistent with a model derived from NMR experiments on 9-aminoacridine binding to dinucleoside phosphates, in which the N-H group is situated in the duplex so as to participate in a hydrogen bond with one base while excluding its complementary partner, thereby provoking mismatching. We also report a strong difference in the dose-response behavior of 9-aminoacridine, quinacrine and a bifunctional derivative of quinacrine.

Aminoacridines↗
PubMed1970

Intercellular effects on development of competence in Bacillus subtilis.

The intercellular transfer of competence during growth under the conditions specified by the transformation procedure of Spizizen was investigated with Bacillus subtilis 168. The rate of competence development as assayed uniformly in medium B was not affected by variations in the cell concentration, although the first appearance of transformants occurred earlier with high cell densities in medium A, approximately in proportion to the onset of the stationary phase in the culture. Growth in the presence of Pronase enhanced the frequency of transformation, but did not detectably alter the kinetics of competence development. The rate of competence increase in physiologically noncompetent cultures was not changed by mixing with competent cultures either in medium A or in medium B; however, an early appearance of transformants was noted in mixed cultures in which the proportion of competent to noncompetent cells prevented exponential growth of the noncompetent strain. These experiments indicate that the normal development of competence in B. subtilis is not mediated by a soluble or loosely bound protein factor capable of transmitting competence directly via cell contact. The onset of competence is thus a function of internal physiological changes which are induced by the overall metabolic state of the culture.

Bacillus subtilis↗