Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Pivot Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Target Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Query: EC:3.1.30.1 (
S1 nuclease
)
3,660
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
The binding of chromosomal protein
HMG1
to a palindromic sequence that can form the cruciform structure in supercoiled DNA and the subsequent effect on the transcription of the sequence were examined with pBR322 and its derivative plasmids. The plasmid DNA under negative supercoiling showed a selective sensitivity to
nuclease S1
.
HMG1
protected against the
nuclease S1
digestion. The results of the filter binding assay indicated that the primary binding target of
HMG1
is the single-stranded region within the cruciform in supercoiled DNA. In the transcription from pBR322 DNA in the absence of
HMG1
, intermediate transcripts of RNA-I, which are encoded from a DNA region containing the palindromic sequence that can form a cruciform, were accumulated with the increase in negative superhelical density whereas the full-length RNA-I was synthesized without an accumulation of intermediate transcripts in the presence of
HMG1
. The intermediates that accumulated in the absence of
HMG1
were elongated to the final product by adding
HMG1
. These results suggest that the cruciform structure formed under negative supercoiling blocks transcription and that
HMG1
can remove the block by altering the DNA conformation to allow the stalled RNA polymerase at the block to resume transcription.
...
PMID:Chromosomal protein HMG1 removes the transcriptional block caused by the cruciform in supercoiled DNA. 170 Sep 77
A high mobility group (HMG) nonhistone protein fraction HMG(1 + 2), composed of
HMG1
and HMG2, was prepared from pig thymus chromatin. In order to examine a possibility that the HMG(1 + 2) participates in the unwinding of the DNA double-helix, DNA hydrolysis assay systems with the endonucleases specific for single-stranded DNA were employed. In the presence of HMG(1 + 2), the hydrolysis of double-stranded DNA by N. crassa endonuclease was markedly promoted, while the hydrolysis of single-stranded DNA was hardly enhanced. The reaction kinetic data showed that the stimulation of the hydrolysis of double-stranded DNA in the presence of HMG(1 + 2) was due to the unwinding of the DNA double-helix by the HMG(1 + 2), and not due to stimulation of enzyme activity of the endonuclease by the protein. The unwinding reactions were dependent on the HMG protein concentration at low weight protein to DNA ratios and reached a maximum at the ratio of 0.025. The region unwound in the whole DNA was partial. Similar results were obtained for experiments with
nuclease S1
. Isolated
HMG1
and HMG2 fractions showed DNA unwinding activity of similar extents. The association constant obtained by fluorescence quenching analysis showed that the HMG(1 + 2) has higher affinity to single-stranded DNA than to double-stranded DNA. The susceptibility to the unwinding differed with the DNA source. These results suggest that HMG(1 + 2) at a low weight protein to DNA ratio binds to some limited double-stranded region in DNA and unwinds the DNA partially.
...
PMID:Unwinding of DNA by nonhistone chromosomal protein HMG(1 + 2) from pig thymus as determined with endonuclease. 632 90
