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T K Misra

Publications and source records attributed to T K Misra.

44 records · Page 3Linked to original sources
PubMed1984

Mercuric ion-resistance operons of plasmid R100 and transposon Tn501: the beginning of the operon including the regulatory region and the first two structural genes.

The mercuric ion-resistance operons of plasmid R100 (originally from Shigella) and transposon Tn501 (originally from a plasmid isolated in Pseudomonas) have been compared by DNA sequence analysis. The sequences for the first 1340 base pairs of Tn501 are given with the best alignment with the comparable 1319 base pairs of R100. The homology between the two sequences starts at base 58 after the end of the insertion sequence IS-1 of R100. The sequences include the transcriptional regulatory region, and the homology is particularly strong in regions just upstream from potential transcriptional initiation sites. The trans-acting regulatory gene merR consists of 180 base pairs in both cases and codes for a highly basic polypeptide of 60 amino acids, which is also rich in serine. The Tn501 and R100 merR genes differ in 25 of the 180 base positions, and the resulting polypeptides differ in seven amino acids. The regulatory region before the major transcription initiation site contains potential -35 and -10 sequences and dyad symmetrical sequences, which may be the merR binding sites for transcriptional regulation. The first structural gene, merT, encodes a highly hydrophobic polypeptide of 116 amino acids. The R100 and Tn501 merT genes differ in 17% of their positions, leading to 14 (12%) amino acid changes. This region had previously been shown to encode a protein governing membrane transport of mercuric ions. The second structural gene, merC, would give a 91 amino acid polypeptide with a hydrophobic amino-terminal segment. The Tn501 and R100 merC genes differ at 37 base positions, leading to 10 amino acid changes.

Amino Acid Sequence↗
PubMed1982

Avian retrovirus pp32 DNA-binding protein. I. Recognition of specific sequences on retrovirus DNA terminal repeats.

The avian retrovirus pp32 protein possesses a DNA-nicking activity which prefers supercoiled DNA as substrate. We have investigated the binding of pp32 to avian retrovirus long terminal repeat (LTR) DNA present in both supercoiled and linear forms. The cloned viral DNA was derived from unintegrated Schmidt-Ruppin A (SRA) DNA. A subclone of the viral DNA in pBR322 (termed pPvuII-DG) contains some src sequences, tandem copies of LTR sequences, and partial gag sequences in the order src-U(3) U(5):U(3) U(5)-gag. Binding of pp32 to supercoiled pPvuII-DG DNA followed by digestion of this complex with a multicut restriction enzyme (28 fragments total) permitted pp32 to preferentially retain on nitrocellulose filters two viral DNA fragments containing only LTR DNA sequences. In addition, pp32 also preferentially retained four plasmid DNA fragments containing either potential promoters or Tn3 "left-end" inverted repeat sequences. Mapping of the pp32 binding sites on viral LTR DNA was accomplished by using the DNase I footprinting technique. The pp32 protein, but not the avian retrovirus alphabeta DNA polymerase, is able to form a unique protein-DNA complex with selected regions of either SRA or Prague A LTR DNAs. Partial DNase I digestion of a 275-base pair SRA DNA fragment complexed with pp32 gives upon electrophoresis in denaturing gels a unique ladder pattern, with regions of diminished DNase I susceptibility from 6 to 10 nucleotides in length, in comparison with control digests in the absence of protein. The binding of pp32 to this fragment also yields enhanced DNase I-susceptible sites that are spaced between the areas protected from DNase I digestion. The protected region of this unique complex was a stretch of 170 +/- 10 nucleotides that encompasses the presumed viral promoter site in U(3), which is adjacent to the src region, extends through U(5), and proceeds past the joint into U(3) for about 34 base pairs. No specific protection or DNase I enhancement by pp32 was observed in experiments with a 435-base pair SRA DNA fragment derived from a part of U(3) and the adjacent src region or a 55-base pair DNA fragment derived from another part of U(3). The DNA sequence of Prague A DNA at the fused LTRs differs from that of SRA DNA. The alteration in the sequence at the juncture of the LTRs prevented pp32 from forming a stable complex in this region of the LTR. Our results are relevant to two aspects of the interaction between pp32 and LTR DNA. First, the pp32 protein in the presence of selected viral DNA restriction fragments possibly forms a higher order oligomer analogous to Escherichia coli DNA gyrase-DNA complexes or eucaryotic nucleosome structures. Second, the specificity of the binding suggests a role for pp32 and the protected DNA sequences in the retrovirus life cycle. The preferred sequences to which pp32 binds include two adjacent 15-base pair inverted terminal repeats at the joint between U(5) and U(3) in SRA DNA. This region is involved in circularization of linear DNA and is perhaps the site that directs integration into cellular DNA.

Avian Leukosis Virus↗
PubMed1979

RNase E, an RNA processing enzyme from Escherichia coli.

An activity, RNase E, was purified about 100-fold from Escherichia coli cells, it can process p5 rRNA from a 9 S RNA molecule which accumulates in a mutant of E. coli defective in the maturation of 5 S rRNA. The enzyme requires Na+, K+, or NH4+, and Mg2+ or Mn2+. The molecular weight of the enzyme is about 70,000 and its pH optimum is 7.6 to 8.0. Its temperature optimum is around 30 degrees C, and it can be irreversibly inactivated at 50 degrees C. It has a very high degree of specificity but the reaction can be inhibited by nonspecific RNAs. We interpret its mode of action in producing p5 RNA as being accomplished in two steps, 9 S RNA is first processed to 7 S and 4 S, and subsequently 7 S is further processed to p5.

Ammonia↗
PubMed1978

Characterization of an endoribonuclease, RNase N, from Escherichia coli.

The properties of the enzyme ribonuclease N were investigated. By comparing the distribution in the cell of RNase N with the bonafide intracellular beta-galactosidase, and the periplasmic alkaline phosphatase enzymes, we showed that RNase N is an intracellular enzyme. Since previous studies suggested that it is an endoribonuclease, it was compared to RNase III, the only other known intracellular endoribonuclease in Escherichia coli. Using homopolymers and co-polymers we found that, while RNase III could digest double-stranded RNA only, RNase N digested single-stranded and double-stranded RNA with similar efficiency. Furthermore, all RNAs used, natural as well as synthetic, were substrates for the enzyme. Using 5 S rRNA as a substrate it was confirmed that the enzyme is an endonuclease. The final products of the reaction of this enzyme are 5'-mononucleotides. The molecular weight of the enzyme is about 120,000 and it seems to contain two subunits which are similar in size. These properties thus differentiate this enzyme from all other known ribonucleases in E. coli.

Alkaline Phosphatase↗
PubMed1976

A new endoribonuclease from Escherichia coli. Ribonuclease N.

A new ribonuclease called RNase N was isolated from Escherichia coli. It is a nonspecific endoribonuclease that can cleave rRNA, poly(U), and poly(C) to small oligonucleotides and 5'-mononucleotides. It requires monovalent cations and is inhibited by divalent cations. It is suggested that this enzyme plays a role in the decay of rRNA,under various starvation conditions and perhaps in the decay of mRNA.

Cations, Monovalent↗
PubMedDate not supplied

DNA sequence analysis of bacterial toxic heavy metal resistances.

Bacterial plasmids have genes that confer highly specific resistances to As, Bi, Cd, Cu, Cr, Hg, Pb, Te, Zn, and other toxic heavy metals. For each toxic cation or anion, generally a different resistance system exists, and these systems may be "linked" together on multiple resistance plasmids. For Cd2+, AsO2-, AsO4(3)-, Hg2+, and organomercurials, DNA sequence analysis has supplemented direct physiological and biochemical experiments to produce sophisticated understanding. The cadA ATPase of S. aureus plasmids is a 727 amino acid membrane ATPase that pumps Cd2+ from the cells as rapidly as it is accumulated. This polypeptide is related by sequence to other cation translocating ATPases, including the membrane K+ ATPases of Escherichia coli and Streptococcus faecalis, the H+ ATPases of yeast and Neurospora, the Na+/K+ ATPases of vertebrate animals, and the Ca2+ ATPases of rabbit muscle. The conserved residues include the aspartyl residue that is phosphorylated, the lysine involved in ATP binding, and the proline within a membrane translocating region. The arsenate and arsenite translocating ATPase consists of 3 polypeptides (from DNA sequence analysis), including a recognizable ATP binding protein (arsA), an integral membrane protein (arsB gene), and a substrate specificity subunit (arsC gene). Inorganic mercury and organomercurial degradation is carried out by a series of about 6 polypeptides, including 2 soluble intracellular enzymes (organomercurial lyase and mercuric reductase). The latter is related by sequence and function to glutathione reductase and lipoamide dehydrogenase of prokaryotes and eukaryotes. These enzymes are dimeric, FAD-containing, NAD(P)H-dependent oxidoreductases. Other recognizable polypeptides in the mer system include a DNA-binding regulatory protein from the merR gene and a Hg2+ transport system consisting of a periplasmic Hg2(+)-binding protein (merP gene) and a membrane protein (merT gene) in gram negative systems.

Amino Acid Sequence↗