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Biomedical subjects

L Bloom

Publications and source records attributed to L Bloom.

30 records · Page 2Linked to original sources
PubMed1980

Isolation and mapping of a mutation in Escherichia coli with altered levels of ribonuclease H.

A mutant of Escherichia coli with altered levels of ribonuclease (RNase) H was isolated after mutagenesis with ethyl methane sulfonate. A procedure for assaying RNase H in partially purified extracts was used to screen approximately 1,500 colonies for variations in RNase H activity. Confirmation of a lower level of RNase H in the mutant was accomplished by analysis of RNase H in sodium dodecyl sulfate-polyacrylamide gels. By Hfr, F', and P1 transduction mapping, the genetic locus responsible for the lower levels of RNase H was located at 5.1 min on the E. coli chromosome. This mutation (rnh) represents a new locus on the E. coli chromosome. The only phenotypic characteristic of this mutation which has been observed to date is the lower level of RNase H (30% of parental values).

Chromosome Mapping↗
PubMed1979

Persistence in the mouse gut as an important factor in oral immunogenicity of strains of V. cholerae.

The immune responses of mice following oral vaccination with two strains of live V. cholerae have been examined. A strain which persisted in the small intestine was a superior local immunogen by comparison with another non-persisting strain. Local persistence and the ability to induce a local immune response appeared to be correlated, since the two vibrio strains elicited identical responses when given parenterally.

Administration, Oral↗
PubMed1979

What, when, and how about why: a longitudinal study of early expressions of causality.

Children's expressions of causality in natural discourse with adults were examined in terms of linguistic, contextual, and pragmatic influences. Specifically, the causal statements, questions, and responses to causal questions of eight 2-3-year-old children were examined in terms of developments in language content, form, and use. With respect to content, the referential and functional uses of causal expressions for both children and adults were to ongoing or imminent situations, with the speaker commenting on his or her intention to act, or requesting the listener to act. The major categories of reference in all three utterance types were negation, direction, and intention. In terms of form, there were (a) increasing use of connectives to link clauses for all the children, and (b) three main patterns of clause order differentiating among the children: cause/effect, effect/cause, and equal use of both orders. The use of expressions of causality developed in the order: child statements less than adult questions less than child responses less than child questions. The relationship of the linguistic context to these developments was found to be one of mutual influence between child and adult. The results are discussed in terms of previous hypotheses concerning (a) causal reasoning (especially those put forth by Piaget, and by Werner & Kaplan in 1963), (b) the relationship between language and conceptual development, (c) the constraints involved in different discourse situations, and (d) variation in child language.

Child Language↗
PubMed1977

Enhancement of opiate binding by various molecular forms of phosphatidylserine and inhibition by other unsaturated lipids.

A study was undertaken on the possible involvement of phospholipids on stereospecific opiate binding to a rat brain membrane fraction comprised mainly of synaptic membranes. The addition of acidic phospholipids such as phosphatidylserine, phosphoinositides, and phosphatidic acid significantly enhanced opiate binding. With the exception of phosphatidylserine, when the acidic phospholipids contained a polyunsaturated acyl group, they were actually inhibitory, along with neutral phospholipids derived from brain. Both the C18:0, C18:1 form (derived from myelin) and the C18:0, C22:6 form of phosphatidylserine (derived from synaptic membranes) produced as much as a 45% enhancement in opiate binding. Unsaturated fatty acids were highly inhibitory, the degree of inhibition being related to the degree of unsaturation. Both phospholipase A and C were inhibitory; and the inhibitory effect of A could not be prevented by albumin or overcome with the addition of phosphatidylserine. With the use of the cross-linking agent, dinitrodifluorobenzene, it could be demonstrated that the phosphatidylserine of synaptic membranes appeared to be preferentially associated with membrane protein. The enhancement of opiate binding by phosphatidylserine diminished with increasing degree of cross-linking.

Animals↗
PubMed1977

Re-examination of small intestinal disposal of Vibrio cholerae in mice.

The rapid disposal of antibody-treated vibrios by peristalsis in whole animal models makes it difficult to obtain clear evidence for a simultaneous intra-intestinal bactericidal effect. In this paper we have re-examined the evidence for direct intra-intestinal killing. We have found that the data can be explained adequately by peristaltic effects without postulating a direct bactericidal action in vivo.

Animals↗