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At least 181 records · Page 10Linked to original sources
PubMed1976

Physical characterization of a ribosomal nucleoprotein complex.

The complex between ribosomal protein L24 and its RNA binding site (that region of the 23S RNA which the protein protects from ribonuclease digestion) has been studied by various physicochemical methods. The RNA is composed of two fragments of about 160 and 140 nucleotides which interact with each other to form the L24 binding site. Circular dichroism spectroscopy suggests that the two interacting fragments have a unique region of secondary structure which is not present in either of the two components alone; hence there are important structural interactions between regions of the RNA which are separated in the primary sequence. Addition of the L24 protein to the RNA site promotes a structural change associated with base unstacking, but with little or no change in the hydrogen-bonded base pairing. Heat activation is not required for complex formation. Thermal denaturation studies reveal a broad featureless transition and the amount of hypochromic change indicates that the RNA site contains less secondary structure than other RNAs such as tRNA and total rRNA. Temperature-jump relaxation measurements on the mechanism of unfolding of the RNA show a concerted melting of the entire secondary and tertiary structure, which is altered upon addition of the protein. A structrual basis for this RNA-protein complex is discussed.

Circular Dichroism↗
PubMed1993

Analysis of a nucleoprotein complex: the synaptosome of gamma delta resolvase.

The gamma delta resolvase protein is one of a large family of transposon-encoded site-specific recombinases. It performs recombination in a DNA-protein complex that contains 12 resolvase protomers and two copies of the 120-base pair DNA substrate, res (each with three binding sites for a resolvase dimer). A derivative of resolvase with altered DNA binding specificity was used to show that the role of resolvase at site I, which contains the crossover point, differs from its role at the other two binding sites. The resolvase dimers that initially bind to site I are the only ones that require the residue Ser10, essential for catalysis of DNA breakage. In addition, these site I-bound dimers do not use a specific interaction between dimers that is required elsewhere in the complex for synapsis of the res sites.

Base Sequence↗
PubMed1998

Amino terminus of reovirus nonstructural protein sigma NS is important for ssRNA binding and nucleoprotein complex formation.

Reovirus nonstructural protein sigma NS exhibits a ssRNA-binding activity thought to be involved in assembling the reovirus mRNAs for genome replication and virion morphogenesis. To extend analysis of this activity, recombinant sigma NS (r sigma NS) was expressed in insect cells using a recombinant baculovirus. In infected-cell extracts, r sigma NS was found in large complexes (> or = 30 S) that were disassembled into smaller, 13-19 S complexes upon treatment with RNase A. R sigma NS also bound to poly(A)-Sepharose beads both before and after purification. Treatment with high salt during purification caused r sigma NS to sediment in even smaller, 7-9 S complexes, consistent with more complete loss of RNA. To localize the RNA-binding site, limited proteolysis was used to fragment the r sigma NS protein. Upon mild treatment with thermolysin, 11 amino acids were removed from the amino terminus of r sigma NS, and the resulting protein no longer bound to poly(A). In addition, when r sigma NS in cell extracts was treated with thermolysin to generate the amino-terminally truncated from, it sedimented at 7-9 S, also consistent with the loss of RNA-binding capacity. To confirm these findings, a deletion mutant lacking amino acids 2-11 was constructed and expressed in insect cells from a recombinant baculovirus. The mutant protein in cell extracts showed greatly reduced poly(A)-binding activity and sedimented as 7-9 S complexes. These data suggest that the first 11 amino acids of sigma NS, which are predicted to form an amphipathic alpha-helix, are important for both ssRNA binding and formation of complexes larger than 7-9 S.

Amino Acid Sequence↗
PubMed1993

The nonspecific DNA-binding and -bending proteins HMG1 and HMG2 promote the assembly of complex nucleoprotein structures.

The mammalian high mobility group proteins HMG1 and HMG2 are abundant, chromatin-associated proteins whose cellular function is not known. In this study we show that these proteins can substitute for the prokaryotic DNA-bending protein HU in promoting the assembly of the Hin invertasome, an intermediate structure in Hin-mediated site-specific DNA inversion. Formation of this complex requires the assembly of the Hin recombinase, the Fis protein, and three cis-acting DNA sites, necessitating the looping of intervening DNA segments. Invertasome assembly is strongly stimulated by HU or HMG proteins when one of these segments is shorter than 104 bp. By use of ligase-mediated circularization assays, we demonstrate that HMG1 and HMG2 can bend DNA extremely efficiently, forming circles as small as 66 bp, and even 59-bp circles at high HMG protein concentrations. In both invertasome assembly and circularization assays, substrates active in the presence of HMG1 contain one less helical turn of DNA compared with substrates active in the presence of HU protein. Analysis of different domains of HMG1 generated by partial proteolytic digestion indicate that DNA-binding domain B is sufficient for both bending and invertasome assembly. We suggest that an important biological function of HMG1 and HMG2 is to facilitate cooperative interactions between cis-acting proteins by promoting DNA flexibility. A general role for HMG1 and HMG2 in chromatin structure is also suggested by their ability to wrap DNA duplexes into highly compact forms.

Animals↗
PubMed1989

A complex nucleoprotein structure involved in activation of transcription of two divergent Escherichia coli promoters.

Initiation of transcription at malEp and malKp, two divergent Escherichia coli promoters, depends on the presence of both CRP, a pleiotropic activator, and MalT, the maltose regulon activator. We carried out in vivo genetic and functional analysis of these promoters and characterized their interaction with MalT and CRP using DNase I footprinting. The functional limits of the promoters are located about 240 base-pairs (bp) upstream of their transcription start sites, which are 271 bp apart. These promoters therefore overlap by about 210 bp. The overlapping region encompasses four CRP-binding sites and at least four MalT-binding sites. Insertions in the centre of this region are tolerated provided that they correspond to an integral number of DNA helix turns. In DNase I footprinting experiments performed on the complex formed by MalT with malEp-malKp, the DNA appears to be wrapped around the protein. We propose a model for the nucleoprotein structure that might be involved in transcription activation at these divergent promoters.

Bacterial Proteins↗
PubMed1986

Changes in the nucleoprotein complexes of a baculovirus DNA during infection.

The nature of the DNA-protein complexes assumed by Autographa californica nuclear polyhedrosis virus (AcNPV) DNA during infection of Spodoptera frugiperda cells was investigated by micrococcal nuclease digestion of infected nuclei. Both parental viral DNA and progeny viral DNA assumed a chromatin-like structure early in infection. By late times (24 hr) p.i., the viral DNA acquired a unique nucleoprotein structure. In addition to fragments of mononucleosome size (185 bp), two subnucleosomal bands of 120 and 90 bp were observed. The subnucleosomal bands contained exclusively viral DNA. No alteration in the nature of the host chromatin structure following AcNPV infection was observed. An examination of the basic chromatin-associated proteins revealed two major viral-induced proteins having molecular weights of 15K and 39K. The induction of the basic 15K protein between 10 and 24 hr p.i. coincided with the appearance of the altered nucleoprotein structure observed by 24 hr p.i. and the cessation of histone synthesis.

Animals↗
PubMed1992

Myc and Max function as a nucleoprotein complex.

The Myc family of oncoproteins are thought to regulate proliferation and differentiation in a wide variety of cell types. Recent studies show that Myc proteins form sequence-specific DNA-binding complexes with Max, a new member of the helix-loop-helix leucine zipper protein class. The properties of the Myc-Max complex suggest a mechanism for Myc's function in both normal and neoplastic cell behavior.

Basic-Leucine Zipper Transcription Factors↗