Student Theses and Dissertations
Date of Award
1985
Document Type
Thesis
Degree Name
Doctor of Philosophy (PhD)
Thesis Advisor
Hidesaburo Hanafusa
Keywords
avian sarcoma virus, UR2, tyrosine kinase, oncogene, growth factor receptor
Abstract
Avian sarcoma virus UR2 is a replication-defective virus that can induce sarcomas in vivo and transforms chicken embryo fibroblasts in culture to a characteristic, extremely elongated morphology. The genome of UR2 contains a 1.2 kb transformation-specific sequence, v-ros, which has a homologous counterpart, c-ros, in normal chicken cellular DNA. The 5' end of v-ros is fused to the helper virus UR2AV-related sequencing coding for one of the viral gag proteins, p19. The fused p19 and ros sequences in UR2 code for a polyprotein of 68 kd, P68gag-ros, which has an associated tyrosine kinase activity. To elucidate the basis of the functional conservation as well as differences between ros and other oncogenes, I sequenced the entire genome of UR2 and compared the predicted amino acid sequence of P68 with other members of the tyrosine kinase family. The results show that ros is 1273 nucleotides in length, including a 65 bp 3' noncoding stretch. ros is joined at its 5' and 3' ends to the 3' region of p19, and the 3' region of gp37, respectively, and replaces the sequences of UR2AV in between. The deduced amino acid sequence for P68 gives a molecular weight of 61,113 daltons and shows that it is closely related to the oncogene family coding for tyrosine protein kinases. However, P68 contains two distinctive hydrophobic regions that are absent in most of the other tyrosine kinases and it has unique amino acid changes and insertions within the conserved domain of the kinases. I also determined the sequence of cellular ros and compared it to viral ros to determine the changes between them that may be responsible for their differential oncogenicity; in addition I have analysed the expression of the cellular gene in both embryonic and adult chickens. The 1.2 kb v-ros sequence is remarkably well conserved when compared with the corresponding region of c-ros. The v-ros sequences are distributed in nine exons of c-ros over a range of 12 kb of DNA. The two differ only by a 9 bp duplication, a single base change not resulting in an amino acid change, and the divergence of their 3' ends. c-ros and v-ros abruptly diverge 36 bp upstream of the v-ros termination codon. The open reading frame of c-ros continues after this divergence and may terminate 34 amino acids downstream, or, more likely, the reading frame is spliced to further 3' coding sequences using a splice donor site 24 nucleotides downstream of the divergence. The v-ros sequence 3' to the divergence was not found in the 3' c-ros sequences in the lambda clone or in helper virus-related sequences. Comparison of the nucleotide sequences of viral and cellular ros suggests the viral ros and Δ gag junction in UR2 was formed by splicing. A 3.1 kb c-ros transcript has been detected in adult muscle tissue and in kidney from chickens only after long exposure of the Northern filters. It appears that the c-ros transcript in kidney is preferentially degraded relative to src, and this may account for the seeming lack of expression in this tissue. In all other tissues examined, and in several cell lines, c-ros transcripts are not detectable. Although the exact function of the cellular ros protein is not known, evidence based on the sequence of the viral and structural genes has enabled us to detect its structural similarity with the EGF and insulin receptors and postulate that ros is a member of a family of growth factor receptors.
License and Reuse Information
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Recommended Citation
Neckameyer, Wendi S., "The Oncogene of Avian Sarcoma Virus UR2 and its Cellular Homologue: Structure, Sequence and Expression" (1985). Student Theses and Dissertations. 463.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/463
Comments
A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy