Date of Award

Spring 1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Biomedical Sciences - Biological Chemistry

Committee Director

Mark S. Elliot

Committee Member

Laura K. Moen

Committee Member

Christopher Osgood

Committee Member

Frank Castora

Abstract

The purpose of this research was to study the effect of the level of tRNA modification with respect to queuine on translational efficiency. Transfer RNA from neoplastic cells is generally deficient with regard to certain hypermodified nucleosides found in normal cells. The hypothesis that was examined is whether or not the altered efficiency of translation can be correlated to the presence of queuine hypomodified tRNA. The loss of queuine in the anticodon may change the interaction of the tRNA's anticodon with its codon. Therefore, the translational complex may stall looking for a rare tRNA, or the stability of the complex adding an amino acid to a peptide chain may be changed by the loss of queuine in the wobble position of the tRNA. Because of the codons contained in the mRNA, these influences may slow or prevent the translation of common genes, but may not affect, or may even increase, the rate for oncogenes or growth-related genes which contain long 5'-untranslated leader sequences. This form of translational control may also be exerted on the minicistrons of the 5'-leader sequences.

This approach used different populations of tRNA to supplement rabbit reticulocyte lysate translation assays. The mRNA was produced in a transcription assay using the bacteriophage T3 polymerase to transcribe the cDNA of genes associated with growth and transformation. This allowed a comparison of the amount of protein produced with normal and hypomodified tRNA. Two genes were used; Nmyc, an oncogene, and murine ornithine decarboxylase, a growth-related gene. These proteins are produced in quantity in cells with hypomodified tRNA and have been shown to be subject to translational controls. Rabbit globin mRNA was used as a control.

Nmyc cDNA was not obtained in a transcription vector. It was cloned into the plasmid pIBI30 downstream of the T3 promoter. Ornithine decarboxylase was obtained in a suitable transcription vector.

The results shown here indicate that queuine levels in tRNA may have only a minor effect in translation of Nmyc and ornithine decarboxylase. However, the effect on globin translation was striking in queuine deficient HFF tRNA, contradicting an earlier study.

DOI

10.25777/w4tv-sg14

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