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Biomedical subjects

A Guha

Publications and source records attributed to A Guha.

At least 145 records · Page 8Linked to original sources
PubMed1978

Isolation of the regulatory segment of the biotin operons of Escherichia coli K-12.

A DNA fragment of 463 base pairs has been isolated by HpaII digestion of the EcoRI cleaved lambdabiot124-10 DNA fragment containing the Escherichia coli biotin gene cluster. This HpaII subfragment contains the biotin regulator region. The biotin regulator DNA has been characterized by electron microscopic heteroduplex analysis, RNA polymerase binding capacity, and the ability to initiate leftward and rightward transcriptions. The two RNA polymerase binding sites are located 63 base pairs and 117 base pairs away from the left end of the HpaII fragment. Both the left- and rightward RNA transcripts have adenosine triphosphates at their 5' end.

Binding Sites↗
PubMed1977

Purification and mode of action of exoribonuclease from bovine brain.

The exoribonuclease in bovine brain has been purified about 900-fold in 10% yield. The molecular weight is about 65,000. The enzyme is free from other ribonucleases of bovine brain. Studies of the mode of action of the enzyme show the following: (a) The enzyme cleaves both oligo- and polyribonucleotides exonucleolytically, initiating nucleolytic attack from the 5'-hydroxyl end to yield 3'-mononucleotides. The enzyme differs from spleen exonuclease in that it does not act on polydeoxyribonucleotides. (b) When the 5'-hydroxyl group is phosphorylated, the enzyme is inactive. (c) The enzymic action is processive in nature; the enzyme hydrolyzes one polynucleotide chain to completion before proceeding to the degradation of another chain.

Animals↗
PubMed1977

Isolation and characterization of the biotin genes of Escherichia coli K-12.

DNA containing the biotin gene cluster, bioABFCD, of E. coli K-12 has been isolated from the EcoRI cleavage products of lambdabiot124-10 phage DNA and subsequently characterized by electron microscopic studies. The biotin-DNA fragment obtained after EcoRI cleavage of the lambdabiot124-10 DNA measures 18.7% lambda DNA length (approx. 9000 base pairs). In addition to the biotin genes, it contains 4.75% and 3.08% lambda phage DNA at the left and right end-points of the bioABFCD cluster, respectively. The two bio promoter sites of the divergently transcribed biotin genes have been visualized under the electron microscope by binding RNA polymerase holoenzyme to the biotin DNA fragment. The two promoters are located at 41% and 43% length of the DNA fragment from its left endpoint. In vitro transcription of RNA from the bio-tin-DNA fragment has been visualized with the electron microscope, but so far no simultaneously transcribing "RNA:DNA" loops of the divergently oriented genes have been observed.

Biotin↗
PubMed1976

Stability of mRNA from the Clostridium sporogenes phage F1.

Polyacrylamide gel electrophoresis was used to study the decay of individual species of mRNA in F1, a bacteriophage specific for the obligate anaerobie Clostridium sporogenes. Immediate early mRNA species had a half-life of 3.5 min, while delayed early and late mRNA had a half-life of between 6 and 8 min.

Anaerobiosis↗
PubMed1975

Solubilization of 2',3'-cyclic nucleotide 3'-phosphohydrolase from bovine brain without detergents.

The enzyme in brain that hydrolyzes 2',3'-cyclic nucleotides to the 2'-mononucleotides has been found by several authors to be concentrated in the myelin fraction. To facilitate further study of the enzyme, one of our objectives has been to develop a method of solubilizing the enzyme without the use of detergents. When an acetone powder from brain white matter is homogenized with 1 M guanidinium chloride in 0.2 M buffer at pH 6, 10(-3) M in EDTA and in dithiothreitol, the enzyme is solubilized. If the guanidinium chloride is removed by dialysis in a single step, the enzyme reprecipitates, but if a fractional precipitation is performed by reducing the guanidinium chloride concentration by dilution, the enzyme remains in solution at 0.2 M guanidinium chloride. The precipitates obtained in this fractionation probably contain constituents which, at low salt concentration, formed a part of an insoluble aggregate, since after removal of the pellet the supernatant solution can be dialyzed free of guanidinium chloride without precipitating the enzymic activity. The enzyme thus prepared remains in the supernatant when centrifuged at 108,000 X g for 3 h and can be submitted to (NH4)2SO4 fractionation and chromatography on carboxymethyl-Sephadex and on hydroxylapatite. The enzyme has thereby been purified 200-fold in about 20% yield.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1975

Correlation matrices for palmar dermatoglyphic traits in twins.

Intraclass correlation values have been studied in a sample of 50 MZ and 50 DZ twins with respect to fourteen palmar dermatoglyphic metric traits in binary combinations. The results confirm the general trends already shown in singleton studies. The shape of the palmar surface does not appear to be significantly correlated with other metric traits. Generally speaking, a large independence has been found between the various traits.

Dermatoglyphics↗
PubMed1975

Development of bacteriophage F1 in Clostridium sporogenes: characterization of RNA transcripts.

RNA transcription was investigated during the development of F1 phage, which is specific for the strict anaerobe Clostridium sporogenes. RNA species transcribed during F1 phage infection were characterized with respect to time of appearance and molecular weight by polyacrylamide gel electrophoresis. Ten mRNA species were characterized, of which five were produced early in infection and five were synthesized late in infection. All the above 10 species were transcribed from one strand of F1DNA, the heavy strand. Two additional mRNA species were transcribed from the light strand of F1 phage DNA later in infection. Throughout the F1 phage infective cycle, rRNA was continuously synthesized by cells of C. sporogenes.

Anaerobiosis↗
PubMed1974

Divergent orientation of transcription from the arginine gene ECBH cluster of Escherichia coli.

Ribonucleic acid (RNA) isolated from Escherichia coli W3350 (F(-), argE(+)C(+)B(+)H(+)), in the absence of l-arginine, hybridizes with the separated leftward (l) and rightward (r) transcribing strands of the arginine transducing phage hphi80dargE(+)C(+)B(+)H(+)ppc(+)imm(lambdacI857) deoxyribonucleic acid (DNA) with a ratio of 30:70, respectively. In the presence of l-arginine and its intermediates, l-ornithine and l-citrulline, RNA transcriptions from both the strands of the argECBH cluster were repressed. The derepressed RNA, when hybridized with the separated strands of hphi80dargEC-I imm(lambda) phage DNA (the arginine genes are inversely inserted in this phage), which has a deletion in gene E and extends to gene C of the argECBH cluster, showed no leftward transcription, whereas the rightward transcription was reduced to about 40% of that when the DNA carrying the entire ECBH cluster was used for hybridization. The hybridization results thus demonstrate that (i) the regulation of the argECBH gene cluster in E. coli is under transcriptional control, (ii) the orientation of transcription is divergent, (iii) E gene transcribes anticlockwise, whereas the rest of the genes, C, B, and H, transcribe clockwise, and (iv) the position of the promoter(s) and operator(s) is located between the E and C genes of the argECBH cluster.

Arginine↗