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Biomedical subjects

M Jayaram

Publications and source records attributed to M Jayaram.

At least 91 records · Page 5Linked to original sources
PubMed1986

Association of reciprocal exchange with gene conversion between the repeated segments of 2-micron circle.

The occurrence of reciprocal exchange of flanking DNA during gene conversion between the repeated segments of the yeast plasmid, 2-micron circle has been examined. The conversion event is induced by making a double-stranded gap within one of the repeats in vitro and allowing the gap to be repaired in vivo. The repair takes place with frequent recombination of flanking markers. Neither the topology of the plasmid substrates (linear or circular) nor the relative orientation of the repeats affects the association rule significantly. These events are reminiscent of meiotic gene conversion between homologous chromosomes but contrast sharply with mitotic or meiotic intrachromosomal gene conversion. It would appear that the difference between the outcomes of intramolecular gene conversion on a chromosome and on a plasmid gapped in vitro does not result from the different physical states of intracellular versus transformed DNA. A gene conversion event in a 2-micron circle : : Tn5 plasmid mediated by the 2-micron circle recombinase (FLP) in vivo, which is formally analogous to the yeast mating type interconversion, often results in recombination of flanking markers. The reaction can be mimicked, in the absence of FLP, by gapping the plasmid within one of the 2-micron circle repeats in vitro and carrying out gap repair in vivo.

DNA Nucleotidyltransferases↗
PubMed1986

Inducible expression of REP1 causes inducible expression of the 2 micron circle stability system.

The yeast plasmid, 2 micron circle, encodes a stability system consisting of the plasmid replication origin, a cis-active locus designated REP3 and two trans-active functions--the products of the REP1 and REP2 genes. We have constructed 2 micron circle derivatives in which the expression of the REP1 gene is placed under the control of the yeast GAL10 promoter. We show that in such plasmids the stability-system is inducible, being turned off by glucose and turned on by galactose. Further, our results unequivocally demonstrate that, of the two potential in-frame ATG codons at which REP1 translation might initiate (as inferred from the 2 micron circle DNA sequence and from the cap site of the major REP1 transcript), the upstream ATG is dispensable without affecting REP1 function. We also illustrate here a simple and general method for constructing in vivo in yeast 2 micron circle analogs which contain desired alterations within specific regions of the 2 micron circle genome.

Base Sequence↗
PubMed1986

Transformation of Phycomyces blakesleeanus to G-418 resistance by an autonomously replicating plasmid.

The fungus, Phycomyces blakesleeanus, shows many well-defined responses to a number of external stimuli. Genetic analysis shows that at least eight genes are involved in Phycomyces sensory transduction. As a first step toward the molecular analysis of these genes and their products, we have developed a transformation protocol for Phycomyces by using a plasmid containing the kanamycin-resistance gene from Tn903 and a Phycomyces DNA fragment capable of supporting autonomous replication in yeast (ARS). Our results demonstrate that the Tn903 gene is expressed in Phycomyces and that the ARS fragment selected in yeast supports autonomous replication in Phycomyces as well.

Drug Resistance, Microbial↗
PubMed1986

Mating type-like conversion promoted by the 2 micrograms circle site-specific recombinase: implications for the double-strand-gap repair model.

Double-strand breaks in DNA are known to promote recombination in Saccharomyces cerevisiae. Yeast mating type switching, which is a highly efficient gene conversion event, is apparently initiated by a site-specific double-strand break. The 2 micrograms circle site-specific recombinase, FLP, has been shown to make double-strand breaks in its substrate DNA. By using a hybrid 2 micrograms circle::Tn5 plasmid, a portion of which resembles, in its DNA organization, the active (MAT) and the silent (HML) yeast mating type loci, it is shown that FLP mediates a conversion event analogous to mating type switching. Whereas the FLP site-specific recombination is not dependent on the RAD52 gene product, the FLP-induced conversion is abolished in a rad52 background. The FLP-promoted conversion in vivo can be faithfully reproduced by making a double-stranded gap in vitro in the vicinity of the FLP site and allowing the gap to be repaired in vivo.

Crosses, Genetic↗
PubMed1986

Substrate recognition by the 2 micron circle site-specific recombinase: effect of mutations within the symmetry elements of the minimal substrate.

The minimal substrate for the 2 microns circle site-specific recombinase FLP consists of a nearly perfect 13-base-pair dyad symmetry with an 8-base-pair core. By using a series of chemically synthesized FLP substrates in in vitro FLP recombination and FLP-binding assays, we have identified four positions within each of the symmetry elements that are important contact points for the FLP protein. Furthermore, the binding and recombination data provide evidence for cooperativity between the two symmetry elements of a substrate and between the symmetry elements of two partner substrates during FLP recombination.

Base Sequence↗
PubMed1985

Two-micrometer circle site-specific recombination: the minimal substrate and the possible role of flanking sequences.

The 2-mum circle DNA of yeast encodes a site-specific recombination system (FLP recombination). The recombination region had been mapped earlier to a 65-base-pair (bp) segment within the 599-bp-long inverted repeats of the molecule. I have shown that the "minimal" FLP substrate resides in a 13-bp dyad symmetry plus an 8-bp core located within the 65-bp recombination region. Further, as determined by different in vivo assays, sequences extraneous to the minimal FLP site and the 65-bp recombination region can affect the efficiency of the recombination reaction.

Base Sequence↗
PubMed1985

Properties of REP3: a cis-acting locus required for stable propagation of the Saccharomyces cerevisiae plasmid 2 microns circle.

Stable propagation of the yeast plasmid 2 microns requires an origin of replication, a cis-active locus designated REP3, and two plasmid-encoded proteins which are the products of the REP1 and REP2 genes. The three REP loci appear to constitute a partitioning system, ensuring equal distribution of plasmid molecules to mother and daughter cells after mitosis. We have localized the REP3 site completely within a segment of five-and-one-half direct tandem repeats of a 62-base-pair unit, bordered by HpaI and AvaI restriction sites within the large unique region of the 2 microns genome. In addition, we find that the repeated elements are functionally distinct. Only a subset of the repeats is necessary to promote full partitioning activity. The other repeats appear to promote plasmid transcription. These results are discussed in the context of a model of plasmid copy control involving titration of a plasmid-specific protein by the repeated elements within REP3.

Base Sequence↗
PubMed1984

Distribution of stuttering in sentences: relationship to sentence length and clause position.

The purpose of this study was to analyze the influence of sentence length and clause position on stuttering in the complex sentences of two languages--English and Kannada. Ten monolingual adult stutterers read 20 sets of sentences while 10 bilingual adult stutterers read 40 sets of sentences (20 sets in each of the two languages). Each set consisted of a short sentence and two long sentences. Results indicated that (a) a clause placed at the beginning of a sentence was stuttered more often than the same clause placed at the end of the sentence and more than the same clause as an isolated sentence; (b) a clause placed at the beginning of a sentence was stuttered more often than the same clause placed at the end of a sentence, irrespective of sentence length; and (c) stuttering occurred more often on the first clause of a sentence than on the second in proportion to the difference in word length between the two clauses. These results suggest that the occurrence of stuttering might be related to the demands that speech makes on motor planning, particularly at the beginning of sentences, and might have significance for the speech breakdown views on stuttering.

Adolescent↗
PubMed1983

Phonetic influences on stuttering in monolingual and bilingual stutterers.

The difficulty stutterers might have with individual sounds was investigated with respect to two modes of speaking (oral reading versus spontaneous speech) and two languages (English versus Kannada). Ten monolingual and ten bilingual stutterers read 16 lists of words (8 in each language). Analysis of stuttering was made with respect to a three-way classification of sounds (vowels, voiceless consonants, and voiced consonants) as well as an eight-way classification (short vowels, long vowels, voiceless stops, voiceless fricatives, voiced stops, voiced fricatives, nasals, and semivowels). Analysis was made with respect to both word-initial and total stuttering. The results indicated that both monolingual and bilingual stutterers were more dysfluent on voiceless consonants and especially on voiceless fricatives, when total stuttering was considered. Results of the analysis of word-initial stuttering on an eight-way classification of sounds showed that the bilingual stutterers stuttered more on the nasal sounds. The results of the bilingual comparison indicated the possibility that the phonetic influences on stuttering might be dependent on the number of languages spoken by the subjects as well as the specific language in which the effects were observed.

Adolescent↗
PubMed1983

The yeast plasmid 2mu circle encodes components required for its high copy propagation.

The yeast plasmid 2mu and certain hybrid plasmids constructed from it are maintained stably and at high copy number in yeast cells. By examining various mutant hybrid 2mu plasmids, we show that these properties require the integrity of four plasmid loci. Two of these, designated REP1 and REP2, are active in trans and correspond to two open coding regions of 2mu. The other two loci are active only in cis and correspond to the origin of replication and to a region, designated REP3, located several hundred bp away from the origin and consisting of direct repeats of a 62 bp sequence. We propose that the REP loci constitute a copy control system that overrides normal cellular restriction on plasmid replication and amplifies the plasmid when copy number is low.

Base Sequence↗
PubMed1983

Yeast plasmid 2-micron circle promotes recombination within bacterial transposon Tn5.

The site-specific recombination system (FLP) encoded by the yeast plasmid 2-micron circle can also act in yeast on the inverted repeats of the bacterial transposon Tn5. The efficiency of this recombination is dependent on the location of Tn5 within the 2-micron circle genome but can be as high as that observed for 2-micron circle itself. Comparison of the DNA sequences between the Tn5 repeat and the 2-micron circle recombination region reveals certain strikingly similar structural features that might be important in the recombination reaction.

Base Sequence↗
PubMed1982

Recombination within the yeast plasmid 2mu circle is site-specific.

The multicopy yeast plasmid, 2mu circle, encodes a specialized recombination system. It contains two regions, each 599 bp in length, that are precise inverted repeats of each other and between which recombination occurs readily. In addition, this recombination requires the product of a 2mu circle gene, designated FLP. By examining the products of FLP-mediated recombination of plasmids containing single insertions within one of the repeated regions, we show that this recombination occurs only at a specific site within the repeat. This result was confirmed from analysis of the ability of plasmids containing various deletions within one of the repeated regions to serve as substrates for FLP-mediated recombination. These experiments limit the recombination site to a sequence of less than 65 bp. In addition, by mutational analysis of the recombination potential of a hybrid plasmid containing the entire 2mu circle genome, we have shown that FLP is only the 2mu circle gene necessary for this site-specific recombination. Finally, we describe a sensitive assay for recombination between the repeated sequences of 2mu circle; using it, we demonstrate that even in the absence of FLP gene product, recombination between the repeats occurs at a low but detectable level during meiosis.

Base Sequence↗
PubMed1981

Replacement of riboflavin by an analogue in the blue-light photoreceptor of Phycomyces.

Under suitable conditions, roseoflavin [7-methyl-8-dimethylamino-10-(1'-D-ribityl)isoalloxazine] replaces riboflavin to about 80% in the photoreceptor of Phycomyces. The substitute-bearing photoreceptor functions with an efficiency of about 0.1% of that of the normal receptor. The substitution is proven by (i) a decrease of the effective light flux by a factor of 4.7, expressed as a corresponding increase in threshold, and (ii) an increase of the effectiveness of 529-nm light relative to 380-nm light. It has also been shown that roseoflavin is taken up by the mycelium, translocated to the sporangiophore, and effectively phosphorylated by the riboflavin kinase of Phycomyces.

Journal Article↗
PubMed1977

Effect of vitamin A nutritional status on the ribonucleic acids of liver, intestinal mucosa and testes of rats.

1. Vitamin A deficiency led to an increase in the oligonucleotide fraction of testes and intestinal mucosa of rats at the expense of high-molecular-weight RNA and 4S RNA, but no such changes were observed in the liver. Retinyl acetate supplementation reversed these effects in both tissues, whereas retinoic acid supplementation was almost equally effective in the mucosa but virtually ineffective in the testes. The ribonuclease activities of all the tissues remained unaffected by the above treatments. 2. The effect of vitamin A deprivation on the acceptor activity of the tRNA of the testes and intestinal mucosa was more pronounced than on the liver tRNA. The testes and mucosal tRNA of the retinoic acid-supplemented rats showed significantly lower charging capacity as compared with the retinyl acetate-supplemented ones. Here also no significant effect was observed on the liver tRNA. 3. Vitamin A deficiency caused a decrease in the percentage of poly(A) in RNA of the mucosa and testes, but not in the liver RNA. The poly(A) contents of both tissues were brought to normal by retinyl acetate supplementation; treatment with retinoic acid led to an appreciable increase in poly(A) in the mucosa, but considerably less increase in poly(A) in the testes. 4. The incorporation of H332PO4 into the rRNA and tRNA of the testes was lowered by vitamin A deficiency, but no such effects was observed in the liver RNA.

Animals↗