PubMed Health⌕ Search

Biomedical subjects

L I Rothblum

Publications and source records attributed to L I Rothblum.

67 records · Page 4Linked to original sources
PubMed1982

Nucleotide sequence of the region between the 18S rRNA sequence and the 28S rRNA sequence of rat ribosomal DNA.

The DNA sequence of the intragenic region of the rat 45S ribosomal RNA precursor was determined. This sequence contains 2282 nucleotides and extends from the conserved EcoR I site near the 3' terminus of 18S rRNA to 69 nucleotides downstream of the 5' terminus of 28S rRNA. The sequences corresponding to 18S and 5.8S rRNA were identified by comparison with previously published data. The 5' terminus of rat 28S rRNA was identified by S1 nuclease protection and reverse transcriptase elongation assays. The internal transcribed spacers were found to be 1066 and 765 nucleotides long and had little homology with those of Xenopus and yeast. Regions of sequence homology between rat and Xenopus were found at the junctions of the internal transcribed spacers with 18S, 5.8S and 28S rRNA. These homologies suggest that these sequences may function as recognition sites for the processing of the ribosomal precursor RNA.

Animals↗
PubMed1982

Isolation and characterization of rat ribosomal DNA clones.

Four EcoRI fragments, which contain the transcribed portion of the rat rDNA repeat, have been isolated from a rat genome library cloned in lambda Charon 4A vector. Three of the fragments, 9.6, 6.7, and 4.5 kb, from clones lambda ChR-B4, lambda Nr-42, and lambda ChR-C4B9, contained part of the 5'-NTS, the 5'-ETS, 18S rDNA, ITS-1, 5.8S rDNA, 28S rDNA and approximately 3.5 kb of the 3'-NTS. Two EcoRI fragments, from clones lambda ChR-B4 and lambda ChR-B7E12, which coded for the 5'-NTS, the ETS, and most of the 18S rDNA, differed by 1 kb near the EcoRI site upstream of the 5' terminus of 18S rRNA. Restriction maps of the cloned DNA fragments were constructed by cleavage of the fragments with various restriction endonucleases and Southern hybridization with 18S, 5.8S, and 28S rRNA. These maps were confirmed and extended by subcloning several regions of the repeat in pBR322.

Animals↗
PubMed1981

Cloning and characterization of a highly reiterated 5.8-kilobase pair nucleolar EcoRI DNA fragment found in Novikoff hepatoma ascites cells.

The DNA of Novikoff hepatoma ascites cells was found to contain a 3.6-megadalton EcoRI restriction fragment, referred to as EcoRI fragment A (Parker et al., 1979). C0t analyses demonstrated an enrichment of fragment A sequences in Novikoff hepatoma genome relative to normal rat liver DNA. This fragment was cloned in lambda gtWES to determine its molecular structure and sequence organization. The DNA from a positive clone was labeled by nick translation and hybridized to a Southern blot of EcoRI digested Novikoff DNA. Distinct hybrids formed with the region corresponding to fragment A. The greater degree of hybridization to the nucleolar fraction suggested a nucleolar enrichment of fragment A. Fragment A has a PstI site approximately 300 base pairs from one terminus which was used to generate mono-5'-32P-labeled fragments. The larger PStI subfragment, 5500 base pairs, labeled at a single terminus, was used to evolve a restriction enzyme map. The 300 base pair fragment was partially sequenced, revealing the presence of a repetitive sequence "island", TT(GTCT)8(GAAT)5G-. C0t analysis, utilizing the purified clone as a probe, confirmed the enrichment of fragment A sequences in the tumor relative to the normal rat liver control.

Animals↗
PubMed1979

Identification of a silver binding protein associated with the cytological silver staining of actively transcribing nucleolar regions.

Nucleoli isolated from Novikoff hepatoma cells were stained with AgNO3 to demonstrate the typical staining of active ribosomal cistrons. Pre-treatment of the nucleoli with 80 mM Tris-HCl (pH 7.5) -- 2.0 M NaCl did not interfere with silver staining. Treatment of the nucleoli with 80 mM Tris-HCl (pH 7.5) -- 0.15 M NaCl did, however, eliminate silver binding. Serial extraction of nucleoli with 2.0 M NaCl buffer followed by 0.15 M NaCl buffer also abolished silver staining. Analysis of the supernatant fraction of these extracts by polyacrylamide gel electrophoresis indicates that, although more than one nucleolar protein can bind silver, only one protein is associated with the staining of active ribosomal cistrons.

Animals↗
PubMed1978

Presence of elongation factor 1 in nuclei and nucleoli of rat liver.

Purified rat liver nuclei contain 11% of the total cellular translation elongation factor 1 activity. Ninety percent of the nuclear EF-1 activity was in the nucleoplasm and 10% was nucleolar. The specific activities of the nuclear and nucleolar EF-1 were 2 to 3 times higher, respectively, than EF-1 activity of the liver homogenate. The presence of EF-1 in the purified nuclei did not result from cytoplasmic contamination since only 0.14% of the cellular lactate dehydrogenase was present in the nuclei. These results provide the first evidence for the presence in the cell nucleus of translational factors of protein synthesis.

Animals↗
PubMed1977

Evidence for coupled synthesis of mRNA for ribosomal proteins and rRNA.

Two-dimensional gel electrophoresis revealed quantitative differences in the 35S-methionine labeled proteins synthesized in vitro in the wheat germ system containing poly A(+) mRNA of normal liver, regenerating liver or Novikoff hepatoma cells. A group of low molecular weight proteins which comigrated with proteins of 40S ribosomal subunits were synthesized in a much greater concentration with the poly A(+) mRNA from the latter two sources. This correlates with increased synthesis of ribosomal proteins in regenerating liver or tumors which is temporally coupled with the increased nucleolar synthesis of rRNA precursors.

Animals↗
PubMed1976

Regulation of mammalian protein synthesis in vivo. Protein synthesis in rat liver and kidney after the administration of sublethal doses of cyclohyximide.

Protein synthesis in vivo was studied at various times after the administration of sublethal doses of cycloheximide to rats. Cycloheximide caused an inhibition, followed by a dose-and time-dependent stimulation, of incorportation of labelled precursor into proteins of the liver and kidney. The stimulation of protein synthesis at 24h was not due to a change of precursor pool or the specific radioactivity of the precursor used. During the stimulatory period, leucine incorporation into various cellular protein fractions varied; incorporation into total nuclear protein was the most affected.

Amino Acids↗