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T O Sitz

Publications and source records attributed to T O Sitz.

At least 19 recordsLinked to original sources
PubMed1993

Adenosine analogs inhibit the guanine-7-methylation of mRNA cap structures.

The adenosine analogs neplanocin A and deazaneplanocin A were observed to inhibit the in vivo guanine-7-methylation of mRNA cap structure using a new assay for hypomethylated RNA. Treatment of cultured mammalian cells with these adenosine analogs resulted in the same extent of hypomethylation of cap structure as did ethionine injection in mice. Neplanocin A and its non-metabolizable analog 3-deazaneplanocin A show the same maximal level of inhibition of methylation suggesting that these adenosine analogs exert their effects by elevating S-adenosylhomocysteine levels rather than by conversion to other inhibitory compounds.

Adenosine↗
PubMed1984

Gene heterogeneity: a basis for alternative 5.8S rRNA processing.

Two bands of 5.8S rRNA were observed when the total RNA isolated from rat or mouse tissue was separated by electrophoresis on high-resolution polyacrylamide gels under denaturing conditions. The minor form, with a lower mobility, represented 15-35% of the total 5.8S rRNA, depending on the source of the tissue. Sequence analysis and the kinetics of formation showed that this minor form is elongated at the 5' end and is not a precursor. The sequence of the minor form was found to be p(C)CGAUA[CG-, five or six nucleotides longer than the major form. The minor 5.8S rRNA constituent also formed a more stable junction complex with 28S rRNA than the shorter major sequence. The rat DNA sequence that corresponds to the additional nucleotides at the 5' end of 5.8S rRNA has been reported to be -CCGTACG-[Subrahmanyam, C. S., Cassidy, B., Busch, H., & Rothblum, L. I. (1982) Nucleic Acids Res. 10, 3667-3680], a sequence which does not contain the extra adenylic acid residue at position 4 found in the minor form. This suggests that the rodent rRNA genes are heterogeneous and that the insertion of an A residue in the ribosomal precursor RNA can generate an alternate processing site.

Animals↗
PubMed1983

Effect of 2'-O-methylation on the structure of mammalian 5.8S rRNAs and the 5.8S-28S rRNA junction.

The mammalian 5.8S rRNA contains a partially 2'-O-methylated uridylic acid residue at position 14 which is largely or entirely methylated in the cytoplasm (Nazar, R.N., Sitz, T.O. and Sommers, K.D. (1980) J. Mol. Biol. 142, 117-121). The effect of this methylation on the 5.8S RNA structure and 5.8-28S rRNA junction was investigated using both chemical and physical approaches. Electrophoretic studies indicated that the free 5.8S rRNA can take on at least two different conformations and that the 2'-O-methylation at U14 restricts the molecule to the more hydrodynamically open form. Structural studies using limited pancreatic or T1 ribonuclease digestion indicated that the methylated conformation was more susceptible to digestion, consistent with a more open tertiary structure. Modification-exclusion studies indicated that the first 29 nucleotides at the 5' end and residues 140 through 158 at the 3' end affect the 5.8S-28S rRNA interaction, supporting previous suggestions that the 5.8S RNA interacts with its cognate high molecular weight component through its termini. These results also suggested that the 2'-O-methylated uridylic acid residue plays a role in the 5.8S-28S rRNA interaction and thermal denaturation studies confirmed this by showing that methylation destabilizes the 5.8S-28S rRNA junction. The 5.8-28S rRNA interaction appears to be more complex than previously believed.

Animals↗
PubMed1983

Significance of S-adenosylmethionine pools in the hypomethylation of ribosomal RNA during the propagation of tissue culture cells and oncogenesis.

The 5.8S rRNA of normal tissues contains a partially 2'-O-methylated uridylic acid residue which is methylated in the cytoplasm and undermethylated in rapidly growing neoplastic tissues (R. N. Nazar, T. O. Sitz, and K. D. Somers, J. Mol. Biol., 142: 117-121, 1980). This difference in methylation was further characterized by examining the effect of cell age or cell culture passage number on the level of methylation of 5.8S RNAs from normal and malignant cell lines and simultaneous changes in intracellular pools of S-adenosylmethionine and S-adenosylhomocysteine. The results indicate that the level of methylation decreases continuously with cell culture passage number as the cells become aneuploid, transformed, or tumorigenic, but there is no direct correlation with the intracellular pools of S-adenosylmethionine or S-adenosylhomocysteine. In contrast, there is a dramatic but inverse increase in the S-adenosylmethionine:S-adenosylhomocysteine ratio which correlates with the decreasing levels of 2'-O-methylation. The significance of these changes in substrate levels to the hypomethylation of 5.8S and other RNAs during oncogenesis is discussed.

Animals↗
PubMed1981

Effect of point mutations on 5.8S ribosomal ribonucleic acid secondary structure and the 5.8S--28S ribosomal ribonucleic acid junction.

Naturally occurring differences in the nucleotide sequences of 5.8S ribosomal ribonucleic acids (rRNAs) from a variety of organisms have been used to study the role of specific nucleotides in the secondary structure and intermolecular interactions of this RNA. Significant differences in the electrophoretic mobilities of free 5.8S RNAs and the thermal stabilities of 5.8S--28S rRNA complexes were observed even in such closely related sequences as those of man, rat, turtle, and chicken. A single base transition from a guanylic acid residue in position 2 in mammalian 5.8S rRNA to an adenylic acid residue in turtle and chicken 5.8S rRNA results both in a more open molecular conformation and in a 5.8S--28S rRNA junction which is 3.5 degrees C more stable to thermal denaturation. Other changes such as the deletion of single nucleotides from either the 5' or the 3' terminals have no detectable effect on these features. The results support secondary structure models for free 5.8S rRNA in which the termini interact to various degrees and 5.8S--28S rRNA junctions in which both termini of the 5.8S molecule interact with the cognate high molecular weight RNA component.

Alkaline Phosphatase↗
PubMed1976

Sequence homologies in mammalian 5.8S ribosomal RNA.

Oligonucleotide products of complete pancreatic or T1 RNase digestion or partial T1 RNase digestion of HeLa cell (human) and MPC-11 cell (mouse) 5.8S rRNA are identical with those obtained from Novikoff hepatoma (rat) 5.8S rRNA except for minor differences at the termini. pCp is the only major 5' terminus of both human and mouse RNAs; both pGp and pCp 5' termini were found in rat 5.8S RNA. Furthermore, HeLa cells contain C-U-U at the 3' end rather than the C-U terminus of mouse and rat. The results indicate that the nucleotide sequence has been highly conserved during the evolution of mammals and suggest that, as reported for 5S rRNA, this sequence is essentially constant throughout the Mammalia.

Base Sequence↗
PubMed1975

Structural analyses of mammalian ribosomal ribonucleic acid and its precursors. Nucleotide sequence of ribosomal 5.8 S ribonucleic acid.

The nucleotide sequence of ribosomal 5.8 S RNA (also known as 7 S or 5.5 S rRNA) from Novikoff hepatoma ascites cells has been determined to be (see article). Estimations of the secondary structure based upon maximized base pairing and the fragments of partial ribonuclease digestion indicate that there may be five base-paired regions in the molecule, three forming a folding of the termini and two forming secondary hairpin loops. The sequence of Novikoff hepatoma 5.8 S rRNA is about 75% homologous with that of yeast 5.8 S rRNA (Rubin, G.M. (1973) J. Biol. Chem. 248, 3860-3875) and similar models for secondary structure are proposed. Both models contain a very stable G-C rich hairpin loop (residues 116 to 138), a less stable A-U-rich hairpin loop (residues 64 to 91) and two symmetrical bulges (residues 15 to 25 and 40 to 44).

Animals↗
PubMed1975

Maturation pathway for Novikoff ascites hepatoma 5.8 S ribosomal ribonucleic acid. Evidence for its presence in 32 S nuclear ribonucleic acid.

Evidence that 32 S nRNA contains 5.8 S rRNA was provided by studies on specific oligonucleotide sequences of these RNA species. Purified 32P-labeled 5.8 and 28 S rRNA and 32 S RNA were digested with T-1 ribonuclease, and the products were fractionated according to chain length by chromatography on DEAE-Sephadex A-25 at neutral pH. The oligonucleotides in Peak 8 were treated with alkaline phosphatase and the products were separated by two-dimensional electrophoresis on cellulose acetate at pH 3.5 and DEAE-paper in 7% formic acid. Seven unique oligonucleotide markers for 5.8 S rRNA including the methylated octanucleotide A-A-U-U-Gm-G-A-Gp were present in 32 S RNA but were not found in 28 S rRNA, indicating that 5.8 S rRNA is directly derived from the 32 S nucleolar precursor. These studies confirm a maturation pathway for rRNA species in which 32 S nucleolar RNA is a precursor of 5.8 S rRNA as well as 28 S rRNA.

Alkaline Phosphatase↗
PubMed1975

Biochemical effects of bleomycin A2 on Novikoff hepatoma ascites cells.

Purified nucleolar DNA was markedly degraded at a concentration of 13 mug/ml by bleomycin A2; bleomycin concentrations 20-30 times greater were required to degrade nucleoplasmic DNA. Whole nuclear DNA was degraded to only a small extent at 13 mug/ml but was markedly degraded at higher bleomycin concentrations. Treatment of the various types of DNA with high concentrations of bleomycin A2 produced low molecular weight (approximately 6S) fragments that were no longer sensitive to degradation by bleomycin A2. Hybridization studies demonstrated a loss of ribosomal DNA sequences from nucleolar DNA treated with bleomycin A2 in vitro. Studies on RNA synthesis in Novikoff hepatoma ascites cells in vitro showed there was a decreased uptake of 32Pi into high molecular weight nuclear RNA in the presence of bleomycin A2. These results indicate that nucleolar function is inhibited by a direct effect of bleomycin A2 on nucleolar DNA.

Ascitic Fluid↗