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Biomedical subjects

P Valenzuela

Publications and source records attributed to P Valenzuela.

At least 91 records · Page 5Linked to original sources
PubMed1981

The interaction of yeast RNA polymerase I and Cibacron blue F3GA.

The interaction between yeast RNA polymerase I and Cibacron blue F3GA has been studied by difference spectrophotometry and column chromatography. The enzyme is reversibly inhibited by the dye. 50% inhibition is obtained with 7.5 x 10(-6) M Cibacron blue. 1 mol Cibacron blue binds per mol enzyme. This interaction, which is inhibited by salt, occurs at a site different from the active site. When RNA polymerase I is chromatographed in Blue dextran-Sepharose columns, two polypeptides, of 48 000 and 36 000 daltons, are dissociated from the enzyme. The resulting enzyme is completely inactive, ATP (5 mM) present in the elution buffer prevents both the dissociation of the polypeptides and the inactivation of the enzyme.

Adenosine Triphosphate↗
PubMed1981

Nucleotide and corresponding amino acid sequences encoded by alpha and beta tubulin mRNAs.

Most of the mRNA sequences coding for alpha and beta tubulin in embryonic chick brain have been determined by sequencing of cloned cDNA copies of these mRNA copies of these mRNAs. From a 1,682-base pair cDNA sequence we have deduced the entire protein sequence for beta tubulin. For alpha tubulin, all but about 38 N-terminal amino acids have been deduced from the cDNA sequence. Although tyrosine has previously been shown to be post-translationally added to the C-terminus of alpha tubulin by a specific ligase, we conclude that the primary post-translational even must be the removal, not the addition of tyrosine because a terminal tyrosine is encoded by the mRNA.

Amino Acid Sequence↗
PubMed1980

Cell-free synthesis of acetylcholine receptor polypeptides.

Messenger RNA coding for acetylcholine receptor peptides has been identified. This polyadenylate [poly(A)+]RNA from Torpedo californica directs, in a cell-free system, the synthesis of peptides 60,000, 51,000, 49,000 41,000, and 35,000 daltons which account for approximately 2 percent of the total synthesized proteins. The results suggest that several different messenger RNA's code for the receptor subunits. These proteins react specifically to antiserum to native acteylcholine receptor, suggesting that the primary translational product has conformational features similar to the native receptor. Further, the results support the idea that there is post-translational modification of receptor subunits as the molecular weights of the cell-free synthesized proteins differ from those of purified receptor subunits.

Acetylcholine↗
PubMed1980

Integration of hepatitis B virus sequences and their expression in a human hepatoma cell.

Hepatitis derived from hepatitis B virus (HBV) infection is endemic throughout the world, but it is particularly prevalent in Asia and Africa. In these areas, demographic studies show a strong coincidence between HBV infection (assayed by HBV antigenic markers) and the incidence of primary liver cancer. On these grounds, a causal link between HBV infection and primary hepatocellular cancer has been proposed. Recently, a human hepatoma cell line (PLC/PRF/5; Alexander cells) has been shown to produce hepatitis B surface antigen (HBsAg). We show here that the Alexander cell line contains at least six (four complete and two partial) hepatitis B viral genomes integrated into high molecular weight host DNA. An analysis using specific probes to fragments of the HBV genome suggests that integration of the virus in most cases occurs at the nicked cohesive end region of the virus. Expression of viral sequences using Northern blots demonstrates the presence of RNA transcripts specific for the surface antigen sequences of HBV DNA and the absence of detectable transcripts corresponding to the hepatitis B core antigen.

Carcinoma, Hepatocellular↗
PubMed1980

The pH dependence of rat liver RNA polymerases I and II.

The effect of pH on the stability and activity of rat liver RNA polymerases I (A) and II (B) has been studied. Both enzymes are irreversibly inactivated in buffer solutions below pH 5.0. Km values of the two enzymes are constant between pH 6.5 and 8.7 but a two -to three- fold increase is observed between pH 8.7 and 9.7. The Vmax versus pH profiles are bell-shaped curves indicating the participation of two ionizing groups with apparent pKa values of 6.5 and 9.8 for enzyme I and 6.7 and 9.9 for enzyme II. Both enzymes are inactivated by photooxidation in the presence of Rose Bengal. It is suggested that the above pKa corresponds to the imidazole of a histidine residue and a amino group of a lysine residue.

Animals↗
PubMed1979

Isolation of yeast tRNALeu genes. DNA sequence of a cloned tRNALeu3 gene.

A library of cloned yeast DNA fragments generated by digestion of yeast DNA with the restriction endonuclease Bam HI has been screened by colony hybridization to total yeast [32P]tRNA. Four hundred colonies carrying yeast tRNA genes were isolated. By hybridization to 125I-tRNALeu3, we have isolated from this collection 14 colonies carrying fragments containing yeast tRNALeu genes. The size of the yeast Bam HI inserts ranged from 2.45 x 10(6) to 14 x 10(6) daltons. One of these fragments was mapped in detail by restriction endonuclease digestion and hybridization to 125I-tRNALeu3. The presence of a tRNALeu3 gene was confirmed by DNA sequence. The results indicate that the tRNALeu3 coding region is not co-linear with the tRNALeu3. An intervening tract of 33 base pairs interrupts the coding sequences 1 base pair past the anticodon coding region. The putative structure of a tRNALeu3 precursor is deduced in which the anticodon base pairs with residues from the intervening sequence.

Base Sequence↗
PubMed1979

Nucleotide sequence of the gene coding for the major protein of hepatitis B virus surface antigen.

DNA extracted from hepatitis B virus Dane particles has been cloned in bacteria using a plasmid vector. A full-length clone has been examined by restriction endonuclease analysis, and the nucleotide sequence of an 892-base pair fragment from cloned hepatitis B viral DNA encoding the surface antigen gene is reported. The amino acid sequence deduced from the DNA indicates that the surface antigens is a protein consisting of 226 amino acids and with a molecular weight of 25,398. The portion of the gene coding for this protein apparently contains no intervening sequences.

Antigens, Surface↗
PubMed1979

Specific gene transcription in yeast nuclei and chromatin by added homologous RNA polymerases I and II.

When treated at pH less than 4.5, yeast nuclei or chromatin lose endogenous RNA synthetic activity. This activity is regained by addition of exogenous RNA polymerases. The specificity of transcription in this system by homologous RNA polymerases I and III has been investigated by gel electrophoresis, hybridization analysis, and RNase T1 mapping. Exogenous RNA polymerase I selectively transcribes rRNA genes. The transcription of these genes by polymerase I is 30- and 8-fold more selective than RNA polymerase III and Escherichia coli polymerase holoenzyme, respectively. Exogenous RNA polymerase III synthesized RNAs similar in size to authentic 5 S RNA, 4.5 S pre-tRNA, and 4 S tRNA. Eleven per cent of this RNA is 5 S RNA as determined by hybridization. Neither polymerase I nor E. coli polymerase synthesizes detectable quantities of RNA in this size range. AT1 ribonuclease digestion of 5 S RNA synthesized by exogenous RNA polymerase III acting on acid-treated chromatin gives a fragment pattern corresponding to that of 5 S RNA. Thus, RNA polymerase III transcribes the entire 5 S gene in this system.

Cell Nucleus↗
PubMed1978

Structure and processing of yeast precursor tRNAs containing intervening sequences.

We have isolated a precursor of yeast tRNATyr and shown that it contains an intervening sequence identical to that found in the gene for tRNATyr. The conformation of pre-tRNATyr is similar to that of mature tRNATyr except for the anticodon loop. The loop is sensitive to endonucleolytic cleavage by S1 nuclease near to the ends of the intervening sequence. This pre-tRNA is functionally inactive as it cannot be aminoacylated and the anticodon is not accessible for hydrogen bonding. A crude nuclear extract from yeast contains an excision-ligase activity which will process pre-tRNATyr into mature tRNATyr.

Anticodon↗