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Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 433 records · Page 24Linked to original sources
PubMed1976

Isolation and characterization of conditional lethal mutants of Escherichia coli defective in transcription termination factor rho.

Polarity suppressor mutants that are conditional lethal for growth have been isolated in E. coli K12. The mutations map between the ilv and cya loci of the E. coli chromosome. Rho factor isolated from one of these ts mutants does not show transcription termination activity at any temperature tested; however, it is found to be temperature sensitive for its poly(C)-dependent ATPase activity. Unlike the previously known polarity suppressor mutants (suA and psu), the rho mutation suppresses all types of polarity. Other interesting properties of these mutants include ultraviolet sensitivity, recombination deficiency, and decreased ability to lysogenize temperate phages lambda and P1. Our results suggest that rho has an essential function in the growth and normal physiology of cells. The rho(ts) mutant allows the growth of phage lambda defective in the N gene. This result supports the model that N gene product prevents transcription termination by antagonizing rho activity.

Adenosine Triphosphatases↗
PubMed1972

Immunochemical studies on the capsular polysaccharide of pneumococcal type IX.

1. In addition to the previously identified components, d-glucose, N-acetyl-d-glucosamine and d-glucuronic acid, the immunologically specific capsular polysaccharide of pneumococcal type IX (polysaccharide S IX) is now found to contain mannosamine and galactosamine, probably as their N-acetyl derivatives. 2. Partial hydrolysis yields a complex mixture of oligosaccharides, several of which have been separated. 3. One of these is alpha-d-glucuronopyranosyl-(1-->3)-d-glucose. It is an inhibitor of the precipitation of antipneumococcal type IX serum by polysaccharide S IX. 4. Two others, d-glucuronopyranosyl-(1-->3)-d-glucosamine and d-glucuronopyranosyl-(1-->3)-d-galactosamine have been identified and a trisaccharide and pentasaccharide partially characterized.

Chromatography, Ion Exchange↗
PubMed1972

Oxidation of the capsular polysaccharide of pneumococcal type IX by periodate.

1. The pneumococcal type IX polysaccharide (polysaccharide S IX) has been oxidized by sodium metaperiodate and reduced by sodium borohydride. Of the constituent monosaccharides, N-acetylglucosamine and N-acetylmannosamine remain unaltered, whereas 40% of the glucose and 90% of the glucuronic acid are oxidized. 2. The effect of oxidation and subsequent reduction on the precipitation of polysaccharide S IX in anti-(pneumococcal) sera is described and interpreted in structural terms. 3. Oligosaccharides produced by oxidation, reduction and hydrolysis with dilute acid have been isolated and partially characterized. 4. The results in this paper and the preceding one (Higginbotham et al., 1972) are used to postulate a possible structure for polysaccharide S IX.

Borohydrides↗
PubMed1969

Immunochemistry of the capsular polysaccharide of an acinetobacter.

The capsular polysaccharide of a strain, BD4, of Acinetobacter calco-aceticus (A.c-a), composed of L-rhamnose and D-glucose, 4:1, precipitates all streptococcal group B antisera tested, as well as streptococcal group G antisera and antipneumococcal (Pn) type XXIII serum. Nonreducing end groups of L-rhamnose, known to be major determinants of the antigens giving rise to these antisera, are thus identified in A.c-a, which also precipitates anti-Pn VI sera. Both the rhamnose and glucose in the capsular polysaccharide (S) of Pn VI are linked 1,3-, as is the rhamnose in Pn S II, which also precipitates anti-Pn VI because of this linkage. A.c-a and S II precipitate the same fraction of anti-Pn VI, identifying a second portion of the rhamnose of A.c-a as 1,3-linked. This is confirmed by the stability of a portion of the rhamnose on oxidation of A.c-a with periodate, and 1,3-linked glucose or a periodate-stable branch point is also indicated in the same way. Two features of the fine structure of A.c-a have thus been established and a third indicated.

Bacteria↗